1/ Phaùt bieåu qui taéc chia moät ña thöùc A cho moät ñôn thöùc B (trong tröôøng hôïp moãi haïng töû cuûa ña thöùc A chia heát cho B).

2/ Laøm tính chia:

a. (2x5 + 3x2 – 4x3) : 2x2

b. (3x2y2 + 6x2y3 – 12xy) : 3xy

3/ Laøm tính nhaân:

(x2 - 4x – 3).(2x2 – 5x + 1)

KIEÅM TRA BAØI KIEÅM TRA BAØI

CUÕCUÕ

Thöù 5 ngaøy 1 thaùng 11 naêm 2007

Thöïc hieän pheùp chia ña thöùcThöïc hieän pheùp chia ña thöùc 2x2x44 - 13x - 13x33 + 15x + 15x22 + 11x + 11x - 3- 3 cho ña thöùccho ña thöùc xx22 - 4x - 3 - 4x - 3..

(1)(2)

2x2x44 - 13x - 13x33 + 15x + 15x22 + 11x - 3 + 11x - 3 xx22 - 4x - 3 - 4x - 32x2x44 xx22

2x2x222x2x44 - 8x- 8x33 - - 6x6x22

––

- 5x- 5x33 + 21x+ 21x22 + 11x - 3+ 11x - 3- 5x- 5x33

xx22

- 5x- 5x

- 5x- 5x33 + 20x+ 20x22 + + 15x15x

––

xx22 - 4x- 4x - 3- 3xx22

xx22

+ 1+ 1

xx22 - 4x- 4x - 3- 3––

00

1. Pheùp chia heát:Ví duï:

Laøm tính chia:Laøm tính chia:

a/ (6xa/ (6x22 + 13x - 5) : (2x + 5) + 13x - 5) : (2x + 5)

b/ (xb/ (x33 - 3x - 3x22 + x - 3) : (x - 3) + x - 3) : (x - 3)

Baøi 48 sbt trang 8:

6x6x22 + 13x - 5 + 13x - 5 2x + 52x + 53x - 13x - 16x6x22 + 15x + 15x– –

- 2x - 5- 2x - 5– –

00- 2x - 5- 2x - 5

xx33 - 3x - 3x22 + x - 3 + x - 3xx33 - 3x - 3x22– –

x - 3x - 3– –

00

x - 3x - 3xx22 + + 11

x - 3x - 3

Thöïc hieän pheùp chia ña thöùcThöïc hieän pheùp chia ña thöùc 5x5x33 - 3x - 3x22 + 7 + 7 cho ña cho ña thöùcthöùc xx22 + 1 + 1..

(1) (2)

5x5x33 - 3x - 3x22 + 7 + 7 xx22 + 1 + 15x5x33 xx22

5x5x5x5x33 + 5x+ 5x––

- 3x- 3x22 - 5x- 5x+ 7+ 7- 3x- 3x22

xx22

- 3- 3

- 3x- 3x22 - 3- 3––

- - 5x5x

+ + 1010

2. Pheùp chia coù dö:Ví duï:Vôùi A, B tuøy yù:Vôùi A, B tuøy yù:

- Toàn taïi duy nhaát Q, R sao cho A = B.Q + Toàn taïi duy nhaát Q, R sao cho A = B.Q + RR

- R = 0R = 0: ta coù pheùp chia heát;: ta coù pheùp chia heát;

- R R 0 0: ta coù pheùp chia coù dö.: ta coù pheùp chia coù dö.

Chuù yù: sgk/31sgk/31

Saép xeáp caùc ña thöùc theo luõy thöøa giaûm daàn Saép xeáp caùc ña thöùc theo luõy thöøa giaûm daàn cuûa bieán roài laøm pheùp chia.cuûa bieán roài laøm pheùp chia.

(x(x44 + x + x22 - 2x - 2x33 - 11 + 13x) : (x - 11 + 13x) : (x22 - 2x + 3) - 2x + 3)

Baøi 50 sbt trang 8:

xx44 - 2x - 2x33 + x + x22 + 13x - 11 + 13x - 11 xx22 - 2x + 3 - 2x + 3xx22 - 2 - 2xx44 - 2x - 2x33 + 3x + 3x22– –

- 2x- 2x22 + 13x - 11 + 13x - 11- 2x- 2x22 + 4x - 6 + 4x - 6– –

9x - 59x - 5

Saép xeáp caùc ña thöùc theo luõy thöøa giaûm daàn Saép xeáp caùc ña thöùc theo luõy thöøa giaûm daàn cuûa bieán roài laøm pheùp chia.cuûa bieán roài laøm pheùp chia.

a/ (xa/ (x33 - 7x + 3 - x - 7x + 3 - x22) : (x - 3)) : (x - 3)

b/ (2xb/ (2x44 - 3x - 3x33 - 3x - 3x22 - 2 + 6x) : (x - 2 + 6x) : (x22 - 2) - 2)

xx33 - x - x22 - 7x + 3 - 7x + 3 x - 3x - 3xx22xx33 - 3x- 3x33– –

2x2x22 - 7x + 3- 7x + 3+ + 2x2x

2x2x22 - 6x- 6x– –

- x- x + 3+ 3

- 1- 1

- x- x + 3+ 3– –

00

Baøi 67 sgk trang 31:

2x2x44 - 3x - 3x33 - 3x - 3x22 + 6x - 2 + 6x - 2 xx22 - 2 - 22x2x222x2x44 - 4x- 4x22– –

- 3x- 3x33 + x+ x22

- 3x- 3x

- 3x- 3x33 + 6x+ 6x– –

xx22 - 2- 2

+ + 11

– –

00

+ 6x - 2+ 6x - 2

xx22 - 2- 2

Cho hai ña thöùc A = 3xCho hai ña thöùc A = 3x44 + x + x33 + 6x - 5 vaø B = x + 6x - 5 vaø B = x22 + + 1. Tìm dö R trong pheùp chia A cho B roài vieát A döôùi 1. Tìm dö R trong pheùp chia A cho B roài vieát A döôùi daïng A = B.Q + Rdaïng A = B.Q + R

Baøi 69 sgk trang 31:

3x3x44 + x + x33 + 6x - 5 + 6x - 5 xx22 + + 113x3x22 + x - 3 + x - 33x3x44 + 3x + 3x22– –

xx33- 3x- 3x22 + 6x - 5 + 6x - 5xx33 + x + x– –

-3x-3x22 - 5x - 5 - 5x - 5– –

3x3x22 - 3 - 3

5x - 25x - 2

Vaäy: 3x4 + x3 + 6x - 5 = (x2 + 1).(3x2 + x - 3) + (5x - 2)

- Hoïc baøi vaø xem laïi hai pheùp chia.Hoïc baøi vaø xem laïi hai pheùp chia.

- Baøi taäp veà nhaø: 70 ñeán 74 sgk.Baøi taäp veà nhaø: 70 ñeán 74 sgk.

- Tieát sau luyeän taäp.Tieát sau luyeän taäp.

AÙp duïng haèng ñaúng thöùc ñaùng nhôù ñeå tính AÙp duïng haèng ñaúng thöùc ñaùng nhôù ñeå tính nhanh.nhanh.

a/ (xa/ (x22 + 2xy + y + 2xy + y22) : (x + y)) : (x + y)

b/ (125xb/ (125x33 + 1) : (5x + 1) + 1) : (5x + 1)

c/ (xc/ (x22 - 2xy + y - 2xy + y22) : (y - x)) : (y - x)

Baøi 68 sgk trang 31:

a/ (xa/ (x22 + 2xy + y + 2xy + y22) : (x + y)) : (x + y)= (x + y)= (x + y)22 : (x + : (x + y)y)= x + = x + yyb/ (125xb/ (125x33 + 1) : (5x + 1) + 1) : (5x + 1) = (5x + 1).(25x= (5x + 1).(25x22 - 5x + 1) : (5x + - 5x + 1) : (5x + 1)1)= 25x= 25x22 - 5x + 1 - 5x + 1

c/ (xc/ (x22 - 2xy + y - 2xy + y22) : (y - x)) : (y - x) = (x - y)= (x - y)22 : - (x - y) : - (x - y)

= - (x – y) = y - x= - (x – y) = y - x