Question

Bài 2: Phân tích đa thức sau thành nhân tử.
a) 3x(x +1) – 5y(x + 1)                                   h) 3x3(2y – 3z) – 15x(2y – 3z)2
b) 3x(x – 6) – 2(x – 6)                                    k) 3x(z + 2) + 5(-x – 2)
c) 4y(x – 1) – (1 – x)                                      l) 18x2(3 + x) + 3(x + 3)
d) (x – 3)3 + 3 – x                                          m) 14x2y – 21xy2 + 28x2y2
e) 7x(x – y) – (y – x)                                      n) 10x(x – y) – 8y(y – x)

Answer 1

a) 3x(x + 1) - 5y(x + 1)

= (x + 1)(3x - 5y)

b) 3x(x - 6) - 2(x - 6)

= (x - 6)(3x - 2)

c) 4y(x - 1) - (1 - x)

= 4y(x - 1) + (x - 1)

= (x - 1)(4y + 1)

d) (x - 3)³ + 3 - x

= (x - 3)³ - (x - 3)

= (x - 3)[(x - 3)² - 1]

= (x - 3)(x - 3 - 1)(x - 3 + 1)

= (x - 3)(x - 4)(x - 2)

Answer 2

e) 7x(x - y) - (y - x)

= 7x(x - y) + (x - y)

= (x - y)(7x + 1)

h) 3x³(2y - 3z) - 15x(2y - 3z)²

= (2y - 3z)[3x³ - 15x(2y - 3x)]

= 3x(2y - 3x)[x² - 5(2y - 3x)]

= 3x(2y - 3x)(x² - 10y + 3x)

= 3x(2y - 3x)(x² + 3x - 10y)

k) 3x(x + 2) + 5(-x - 2)

= 3x(x + 2) - 5(x + 2)

= (x + 2)(3x - 5)

l) 18x²(3 + x) + 3(x + 3)

= (x + 3)(18x² + 3)

= 3(x + 3)(6x² + 1)

m) 7x(x - y) - (y - x)

= 7x(x - y) + (x - y)

= (x - y)(7x + 1)

n) 10x(x - y) - 8y(y - x)

= 10x(x - y) + 8y(x - y)

= (x - y)(10x + 8y)

= 2(x - y)(5x + 4y)