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CC DNG TON C BN LP 4

PHN KIN THC

KIN THC CN GHI NH

+S V CH S

I. Kin thc cn ghi nh

1. Dng 10 ch s vit s l: 0, 1, 2, 3, 4, 5, 6, 7, 8 ,9.

2. C 10 s c 1 ch s: (T s 0 n s 9)

C 90 s c 2 ch s: (t s 10 n s 99)

C 900 s c 3 ch s: (t s 100 n 999)

C 9000 s c 4 ch s: (t s 1000 n 9999)

3. S t nhin nh nht l s 0. Khng c s t nhin ln nht.

4. Hai s t nhin lin tip hn (km) nhau 1 n v.

5. Cc s c ch s tn cng l 0, 2, 4, 6, 8 gi l s chn. Hai s chn lin

tip hn (km) nhau 2 n v.

6. Cc s c ch s tn cng l 1, 3, 5, 7, 9 gi l s l. Hai s l lin tip

hn (km) nhau 2 n v.

A. PHP CNG

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1. a + b = b + a

2. (a + b) + c = a + (b + c)

3. 0 + a = a + 0 = a

4. (a - n) + (b + n) = a + b

5. (a - n) + (b - n) = a + b - n x 2

6. (a + n) + (b + n) = (a + b) + n x 2

7. Nu mt s hng c gp ln n ln, ng thi cc s hng cn li c

gi nguyn th tng c tng ln mt s ng bng (n - 1) ln s hng

c gp ln .

8. Nu mt s hng b gim i n ln, ng thi cc s hng cn li c gi

nguyn th tng b gim i mt s ng bng (1 - ) s hng b gim i .

9. Trong mt tng c s lng cc s hng l l l th tng l mt s l.

10. Trong mt tng c s lng cc s hng l l chn th tng l mt s

chn.

11. Tng ca cc s chn l mt s chn.

12. Tng ca mt s l v mt s chn l mt s l.

13. Tng ca hai s t nhin lin tip l mt s l.

B. PHP TR

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1. a - (b + c) = (a - c) - b = (a - b) - c

2. Nu s b tr v s tr cng tng (hoc gim) n n v th hiu ca chng

khng i.

3. Nu s b tr c gp ln n ln v gi nguyn s tr th hiu c tng

thm mt s ng bng (n -1) ln s b tr. (n > 1).

4. Nu s b tr gi nguyn, s tr c gp ln n ln th hiu b gim i (n -

1) ln s tr. (n > 1).

5. Nu s b tr c tng thm n n v, s tr gi nguyn th hiu tng ln

n n v.

6. Nu s b tr tng ln n n v, s tr gi nguyn th hiu gim i n n

v.

C.PHP NHN

1. a x b = b x a

2. a x (b x c) = (a x b) x c

3. a x 0 = 0 x a = 0

4. a x 1 = 1 x a = a

5. a x (b + c) = a x b + a x c

6. a x (b - c) = a x b - a x c

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7. Trong mt tch nu mt tha s c gp ln n ln ng thi c mt tha

s khc b gim i n ln th tch khng thay i.8. Trong mt tch c mt

tha s c gp ln n ln, cc tha s cn li gi nguyn th tch c gp

ln n ln v ngc li nu trong mt tch c mt tha s b gim i n ln, cctha

s cn li gi nguyn th tch cng b gim i n ln. (n > 0)

9. Trong mt tch, nu mt tha s c gp ln n ln, ng thi mt tha s

c gp ln m ln th tch c gp ln (m x n) ln. Ngc li nu trong

mt tch mt tha s b gim i m ln, mt tha s b gim i n ln th tchb gim i (m x n) ln. (m v n khc 0)10. Trong mt tch, nu mt tha s

c tng thm a n v, cc tha s cn li gi nguyn th tch c tng

thm a ln tch cc tha s cn li.

11. Trong mt tch, nu c t nht mt tha s chn th tch chn.

12.Trong mt tch, nu c t nht mt tha s trn chc hoc t nht mt

tha s c tn cng l 5 v c t nht mt tha s chn th tch c tn cng l

0.13. Trong mt tch cc tha s u l v c t nht mt tha s c tn cng

l 5 th tch c tn cng l 5.

D. PHP CHIA

1. a : (b x c) = a : b : c = a : c : b (b, c > 0)

2. 0 : a = 0 (a > 0)

3. a : c - b : c = ( a - b) : c (c > 0)

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4. a : c + b : c = (a + b) : c (c > 0)

5. Trong php chia, nu s b chia tng ln (gim i) n ln (n > 0) ng thi

s chia gi

nguyn th thng cng tng ln (gim i) n ln.

6. Trong mt php chia, nu tng s chia ln n ln (n > 0) ng thi s b

chia gi nguyn th thng gim i n ln v ngc li.7. Trong mt php

chia, nu c s b chia v s chia u cng gp (gim) n ln (n > 0) th

thng khng thay i.8. Trong mt php chia c d, nu s b chia v s

chia cng c gp (gim) n ln (n > 0) th s d cng c gp (gim ) n

ln.

E. TNH GI TR CA BIU THC

1. Biu thc khng c du ngoc n ch c php cng v php tr (hoc ch

c php nhn v php chia) th ta thc hin cc php tnh theo th t t tri

sang phi.

V d: 542 + 123 - 79 482 x 2 : 4

= 665 - 79 = 964 : 4

= 586 = 241

2. Biu thc khng c du ngoc n, c cc php tnh cng, tr, nhn, chia

th ta thc hin cc php tnh nhn, chia trc ri thc hin cc php tnh

cng tr sau.

V d: 27 : 3 - 4 x 2

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= 9 - 8 = 1

3. Biu thc c du ngoc n th ta thc hin cc php tnh trong ngoc n

trc, cc php tnh ngoi du ngoc n sau

V d: 25 x (63 : 3 + 24 x 5)

= 25 x (21 + 120)

=25 x 141

=3525