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8/9/2019 phuongtrinhlogarit
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LUYN TPGII PHNG TRNH
LNGGIC
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx
Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 2/ 15
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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tvn
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx
Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 3/ 15
Trong bi trc chng ta hc phng trnh lgaritv cch gii mt s phng trnh lgarit thng gp.Hm nay chng ta s luyn tp v cch gii cc phngtrnh lgarit.
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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Phngphpavcngcs
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx
Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 4/ 15
Vd1. Gii phng trnhlog3 3x + log9 x + log27 x = 12.
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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Phngphpavcngcs
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx
Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 4/ 15
Vd1. Gii phng trnhlog3 3x + log9 x + log27 x = 12.
Hng gii. t iu kin x > 0.Bin i a v dng phng trnh n log3 x.
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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Phngphptnsph
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx
Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 5/ 15
Phng php: t iu kin cc biu thc ca phng trnh
c ngha.
La chn n ph cho phng trnh v iu kincho cc n ph.
Gii phng trnh mi nhn c. Kim tra tnh hp l.
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx
Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 6/ 15
Vd2. Gii phng trnhlog2 (3
x 1). log2 (2.3x 2) = 2.
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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8/9/2019 phuongtrinhlogarit
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8/9/2019 phuongtrinhlogarit
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LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx
Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 6/ 15
Vd2. Gii phng trnhlog2 (3
x 1). log2 (2.3x 2) = 2.
Hng gii. Phng trnh tng ng vilog2 (3
x 1).[1 + log2 (3x 1) = 2.
iu kin 3x 1 > 0 x > 0.
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx
Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 6/ 15
Vd2. Gii phng trnhlog2 (3
x 1). log2 (2.3x 2) = 2.
Hng gii. Phng trnh tng ng vilog2 (3
x 1).[1 + log2 (3x 1) = 2.
iu kin 3x 1 > 0 x > 0.t t = log2 (3x 1), phng trnh tr thnh
t(t + 1) = 2
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx
Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 6/ 15
Vd2. Gii phng trnhlog2 (3
x 1). log2 (2.3x 2) = 2.
Hng gii. Phng trnh tng ng vilog2 (3
x 1).[1 + log2 (3x 1) = 2.
iu kin 3x 1 > 0 x > 0.t t = log2 (3x 1), phng trnh tr thnh
t(t + 1) = 2
t = 1
t =
2
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx
Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 6/ 15
Vd2. Gii phng trnhlog2 (3
x 1). log2 (2.3x 2) = 2.
Hng gii. Phng trnh tng ng vilog2 (3
x 1).[1 + log2 (3x 1) = 2.
iu kin 3x 1 > 0 x > 0.t t = log2 (3x 1), phng trnh tr thnh
t(t + 1) = 2
t = 1
t =
2
x =
1
x = log3
5
4
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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Phngphpsdngtnhniu
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx
Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 7/ 15
Vd3. Gii phng trnhlog2 (x
2 4) + x = 3 + log2 (x + 2).
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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Phngphpsdngtnhniu
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx
Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 7/ 15
Vd3. Gii phng trnhlog2 (x
2 4) + x = 3 + log2 (x + 2).
Hng gii. iu kin
x2 4 > 0x + 2 > 0
x > 2.
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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Phngphpsdngtnhniu
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 7/ 15
Vd3. Gii phng trnhlog2 (x
2 4) + x = 3 + log2 (x + 2).
Hng gii. iu kin
x2 4 > 0x + 2 > 0
x > 2.
Phng trnh tng ng vi
log2 (x 2) = 3 x.
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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Phngphpsdngtnhniu
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 7/ 15
Vd3. Gii phng trnhlog2 (x
2 4) + x = 3 + log2 (x + 2).
Hng gii. iu kin
x2 4 > 0x + 2 > 0
x > 2.
Phng trnh tng ng vi
log2 (x 2) = 3 x.
Nhn thyx = 3 l nghim.
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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Phngphpsdngtnhniu
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 7/ 15
Vd3. Gii phng trnhlog2 (x
2 4) + x = 3 + log2 (x + 2).
Hng gii. iu kin
x2 4 > 0x + 2 > 0
x > 2.
Phng trnh tng ng vi
log2 (x 2) = 3 x.
Nhn thyx = 3 l nghim.
Vi x > 3 th log2 (x 2) > log2 1 = 0, v 3 x < 0. Do phng trnh v nghim.
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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Phngphpsdngtnhniu
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 7/ 15
Vd3. Gii phng trnhlog2 (x
2 4) + x = 3 + log2 (x + 2).
Hng gii. iu kin
x2 4 > 0x + 2 > 0
x > 2.
Phng trnh tng ng vi
log2 (x 2) = 3 x.
Nhn thyx = 3 l nghim.
Vi x > 3 th log2 (x 2) > log2 1 = 0, v 3 x < 0. Do phng trnh v nghim.Vi x < 3 th log2 (x 2) < log2 1 = 0, v 3 x > 0. Do phng trnh v nghim.
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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Phngphpsdngtnhniu
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 7/ 15
Vd3. Gii phng trnhlog2 (x
2 4) + x = 3 + log2 (x + 2).
Hng gii. iu kin
x2 4 > 0x + 2 > 0
x > 2.
Phng trnh tng ng vi
log2 (x 2) = 3 x.
Nhn thyx = 3 l nghim.
Vi x > 3 th log2 (x 2) > log2 1 = 0, v 3 x < 0. Do phng trnh v nghim.Vi x < 3 th log2 (x 2) < log2 1 = 0, v 3 x > 0. Do phng trnh v nghim.
Vy phng trnh c nghim duy nht x = 3.
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Phng php nh gi
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 8/ 15
S dng:s Tam thc bc hai.
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Phng php nh gi
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 8/ 15
S dng:s Tam thc bc hai.
s
Cc BT c bn nh Cauchy, Bunhiacopsky.
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Phng php nh gi
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 8/ 15
S dng:s Tam thc bc hai.
s
Cc BT c bn nh Cauchy, Bunhiacopsky.s Tnh cht ca gi tr tuyt i.
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LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 9/ 15
Vd4. Gii phng trnhlog3
2 (
4 x +
x + 5) = 1.
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 9/ 15
Vd4. Gii phng trnhlog3
2 (
4 x +
x + 5) = 1.
Hng gii. iu kin5 x 4.
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 9/ 15
Vd4. Gii phng trnhlog3
2 (
4 x +
x + 5) = 1.
Hng gii. iu kin5 x 4.Theo BT Bunhiacopsky ta c
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LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 9/ 15
Vd4. Gii phng trnhlog3
2 (
4 x +
x + 5) = 1.
Hng gii. iu kin5 x 4.Theo BT Bunhiacopsky ta c
4
x +
x + 5
(12 + 12)(4
x + x + 5) = 3
2.
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 9/ 15
Vd4. Gii phng trnhlog3
2 (
4 x +
x + 5) = 1.
Hng gii. iu kin5 x 4.Theo BT Bunhiacopsky ta c
4
x +
x + 5
(12 + 12)(4
x + x + 5) = 3
2.
Suy ra log32 (
4 x +x + 5) < log32 3
2 = 1.
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 9/ 15
Vd4. Gii phng trnhlog3
2 (
4 x +
x + 5) = 1.
Hng gii. iu kin5 x 4.Theo BT Bunhiacopsky ta c
4
x +
x + 5
(12 + 12)(4
x + x + 5) = 3
2.
Suy ra log32 (
4 x +x + 5) < log32 3
2 = 1.
Du = xy ra khi v ch khi4
x
1 =
x
+ 51 x = 12 .
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LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 9/ 15
Vd4. Gii phng trnhlog3
2 (
4 x +
x + 5) = 1.
Hng gii. iu kin5 x 4.Theo BT Bunhiacopsky ta c
4
x +
x + 5
(12 + 12)(4
x + x + 5) = 3
2.
Suy ra log32 (
4 x +x + 5) < log32 3
2 = 1.
Du = xy ra khi v ch khi4
x
1 =
x
+ 51 x = 12 . Vyx = 12 l nghimduy nht ca bi ton.
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Phng php th
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 10/ 15
Vd5. Hy bin lun theo m s nghim ca phngtrnhlg (m x2) = lg (x2 3x + 2).
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Phng php th
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 10/ 15
Vd5. Hy bin lun theo m s nghim ca phngtrnhlg (m x2) = lg (x2 3x + 2).
Hng gii. Phng trnh tng ng vix2 3x + 2 > 0m
x2 = x2
3x + 2
x > 2 x < 12x2
3x + 2 = m
2
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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Phng php th
LUYN TP GIIPHNG TRNHLNG GICxt vn x Phng php av cng c sx Phng php tn s phx
x Phng php sdng tnh n iux Phng phpnh gi
x
x Phng php th
Cc hot ng
Gii phng trnh lgarit-Diendankienthuc.net slide th 10/ 15
Vd5. Hy bin lun theo m s nghim ca phngtrnhlg (m x2) = lg (x2 3x + 2).
Hng gii. Phng trnh tng ng vix2 3x + 2 > 0m
x2 = x2
3x + 2
x > 2 x < 12x2
3x + 2 = m
2
S nghim ca phng trnh cho l s honh giao im ca parabol y = 2x2 3x + 2 vi ng
thng y = m.
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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Cc hot ng
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 11/ 15
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Hotng1
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 12/ 15
Tm phng php gii cc phng trnh sau:
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Hotng1
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 12/ 15
Tm phng php gii cc phng trnh sau:1)
log2 x
log4 2x=
log8 9x
log16 8x.
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Hotng1
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 12/ 15
Tm phng php gii cc phng trnh sau:1)
log2 x
log4 2x=
log8 9x
log16 8x.
2) log5(x2 + 1) + log1/5 5 = log5 (x + 2)
2log1/25 x
2.
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Hotng1
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 12/ 15
Tm phng php gii cc phng trnh sau:1)
log2 x
log4 2x=
log8 9x
log16 8x.
2) log5(x2 + 1) + log1/5 5 = log5 (x + 2)
2log1/25 x
2.
3) (x + 2) log23(x + 1) + 4(x + 1) log3 (x + 1) 16 = 0.
http://diendankienthuc.net/diendan/http://diendankienthuc.net/diendan/8/9/2019 phuongtrinhlogarit
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Hotng1
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 12/ 15
Tm phng php gii cc phng trnh sau:1)
log2 x
log4 2x=
log8 9x
log16 8x.
2) log5(x2 + 1) + log1/5 5 = log5 (x + 2)
2log1/25 x
2.
3) (x + 2) log23(x + 1) + 4(x + 1) log3 (x + 1) 16 = 0.4) log2(x + 3log6 x) = log6 x.
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Hotng1
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 12/ 15
Tm phng php gii cc phng trnh sau:1)
log2 x
log4 2x=
log8 9x
log16 8x.
2) log5(x2 + 1) + log1/5 5 = log5 (x + 2)
2log1/25 x
2.
3) (x + 2) log23(x + 1) + 4(x + 1) log3 (x + 1) 16 = 0.4) log2(x + 3log6 x) = log6 x.5) Tu theo m hy bin lun s nghim ca phngtrnh
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Hotng1
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 12/ 15
Tm phng php gii cc phng trnh sau:1)
log2 x
log4 2x=
log8 9x
log16 8x.
2) log5(x2 + 1) + log1/5 5 = log5 (x + 2)
2log1/25 x
2.
3) (x + 2) log23(x + 1) + 4(x + 1) log3 (x + 1) 16 = 0.4) log2(x + 3log6 x) = log6 x.5) Tu theo m hy bin lun s nghim ca phngtrnh
logm2+2(1 x2 + m2) = logm2+2[2(1 + x + m)].
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Hotng2
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 13/ 15
Thi ua gii cc phng trnh sau:
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Hotng2
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 13/ 15
Thi ua gii cc phng trnh sau:log5
5
x
log5 5x
+ log25 x = 1.
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Hotng2
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 13/ 15
Thi ua gii cc phng trnh sau:log5
5
x
log5 5x
+ log25 x = 1.
Li gii.
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Hotng2
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 13/ 15
Thi ua gii cc phng trnh sau:log5
5
x
log5 5x
+ log25 x = 1.
Li gii.iu kin x > 0.
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Hotng2
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 13/ 15
Thi ua gii cc phng trnh sau:log5
5
x
log5 5x
+ log25 x = 1.
Li gii.iu kin x > 0. P T 1 log5 x1 + log5 x
+ log25 x = 1.
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Hotng2
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 13/ 15
Thi ua gii cc phng trnh sau:log5
5
x
log5 5x
+ log25 x = 1.
Li gii.iu kin x > 0. P T 1 log5 x1 + log5 x
+ log25 x = 1.
t t = log5
x th phng trnh tr thnh
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Hotng2
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 13/ 15
Thi ua gii cc phng trnh sau:log5
5
x
log5 5x
+ log25 x = 1.
Li gii.iu kin x > 0. P T 1 log5 x1 + log5 x
+ log25 x = 1.
t t = log5
x th phng trnh tr thnh
1 t1 + t
+ t2 = 1 t3 + t2 2t = 0 t = 0 t = 1 t = 2.
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Hotng2
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 13/ 15
Thi ua gii cc phng trnh sau:log5
5
x
log5 5x
+ log25 x = 1.
Li gii.iu kin x > 0. P T 1 log5 x1 + log5 x
+ log25 x = 1.
t t = log5
x th phng trnh tr thnh
1 t1 + t
+ t2 = 1 t3 + t2 2t = 0 t = 0 t = 1 t = 2.
T tm c x = 1, x = 5, x = 125
.
H 3
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Hotng3
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 14/ 15
Tm sai lm trong li gii bi ton sau v a ra li giing:
H 3
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Hotng3
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 14/ 15
Tm sai lm trong li gii bi ton sau v a ra li giing:Gii phng trnh
H 3
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Hotng3
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 14/ 15
Tm sai lm trong li gii bi ton sau v a ra li giing:Gii phng trnh
32
log 14
(x + 2)2 3 = log 14
(4 x)3 + log 14
(x + 6)3
H t 3
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Hotng3
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 14/ 15
Tm sai lm trong li gii bi ton sau v a ra li giing:Gii phng trnh
32
log 14
(x + 2)2 3 = log 14
(4 x)3 + log 14
(x + 6)3
Li gii.
H t 3
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Hotng3
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 14/ 15
Tm sai lm trong li gii bi ton sau v a ra li giing:Gii phng trnh
32
log 14
(x + 2)2 3 = log 14
(4 x)3 + log 14
(x + 6)3
Li gii.iu kin
(x + 2)2 > 04 x > 0x + 6 > 0
H t 3
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Hotng3
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 14/ 15
Tm sai lm trong li gii bi ton sau v a ra li giing:Gii phng trnh
32
log 14
(x + 2)2 3 = log 14
(4 x)3 + log 14
(x + 6)3
Li gii.iu kin
(x + 2)2 > 04 x > 0x + 6 > 0
6 < x < 4, x = 2.
H t 3
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Hotng3
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 14/ 15
Tm sai lm trong li gii bi ton sau v a ra li giing:Gii phng trnh
32
log 14
(x + 2)2 3 = log 14
(4 x)3 + log 14
(x + 6)3
Li gii.iu kin
(x + 2)2 > 04 x > 0x + 6 > 0
6 < x < 4, x = 2.
Phng trnh tng ng vi
Hotng3
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Hotng3
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 15/ 15
3log1/4(x + 2) 3 = 3 log1/4(4 x) + 3 log1/4(x + 6) log1/4
x + 2
(4
x)(6 + x)= 1
x + 2(4 x)(6 + x) =
1
4
x2 + 6x
16 = 0
x =
8 (loi)
x = 2.
Vy phng trnh cho c nghim x = 2.
Hotng3
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Hotng3
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 15/ 15
3log1/4(x + 2) 3 = 3 log1/4(4 x) + 3 log1/4(x + 6) log1/4
x + 2
(4
x)(6 + x)= 1
x + 2(4 x)(6 + x) =
1
4
x2 + 6x
16 = 0
x =
8 (loi)
x = 2.
Vy phng trnh cho c nghim x = 2.
Hotng3
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Hotng3
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 15/ 15
3log1/4(x + 2) 3 = 3 log1/4(4 x) + 3 log1/4(x + 6) log1/4
x + 2
(4
x)(6 + x)= 1
x + 2(4 x)(6 + x) =
1
4
x2 + 6x
16 = 0
x =
8 (loi)
x = 2.
Vy phng trnh cho c nghim x = 2.
Hotng3
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Hotng3
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
Gii phng trnh lgarit-Diendankienthuc.net slide th 15/ 15
3log1/4(x + 2) 3 = 3 log1/4(4 x) + 3 log1/4(x + 6) log1/4
x + 2
(4
x)(6 + x)= 1
x + 2(4 x)(6 + x) =
1
4
x2 + 6x
16 = 0
x =
8 (loi)
x = 2.
Hotng3
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Hotng3
LUYN TP GIIPHNG TRNHLNG GIC
Cc hot ngxHot ng 1xHot ng 2
xHot ng 3xHot ng 3
3log1/4(x + 2) 3 = 3 log1/4(4 x) + 3 log1/4(x + 6) log1/4
x + 2
(4
x)(6 + x)= 1
x + 2(4 x)(6 + x) =
1
4
x2 + 6x
16 = 0
x =
8 (loi)
x = 2.
Vy phng trnh cho c nghim x = 2.