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222-9+11+12:2*14+14 = ? ( )

## Toán Lớp 8: Phân tích đa thức sau thành nhân tử a) 3x(x + 1) – y(x + 1) b) x² + 5x – xy – 5y c) x² – 4y² – 6x +9 d) 6x² – 7x + 2

Toán Lớp 8: Phân tích đa thức sau thành nhân tử
a) 3x(x + 1) – y(x + 1)
b) x² + 5x – xy – 5y
c) x² – 4y² – 6x +9
d) 6x² – 7x + 2

1. a) 3x(x + 1) – y(x + 1)
=(x+1)(3x-y)
b) x² + 5x – xy – 5y
=(x²- xy )+( 5x  – 5y)
=x(x-y)+5(x-y)
=(x-y)(x+5)
c) x² – 4y² – 6x +9
=(x²- 6x +9) – 4y²
=(x-3)^2-(2y)^2
=(x-3-2y)(x-3+2y)
d) 6x² – 7x + 2
=6x² – 3x-4x + 2
=(6x² – 3x)-(4x – 2)
=3x(2x – 1)-2(2x – 1)
=(2x-1)(3x-2)

2. a) $3x\left(x+1\right)-y\left(x+1\right)$
$3x^2+3x-y\left(x+1\right)$
$=3x^2+3x-xy-y$
b) $x^2+5x-xy-5y$
$=\left(x^2+5x\right)+\left(-xy-5y\right)$
$=x\left(x+5\right)-y\left(x+5\right)$
$=\left(x+5\right)\left(x-y\right)$
c) $x^2-4y^2-6x+9$
$=\left(x-3\right)^2-4y^2$
$=\left(x-3\right)^2-\left(2y\right)^2$
$=\left(\left(x-3\right)+2y\right)\left(\left(x-3\right)-2y\right)$
$=\left(x-3+2y\right)\left(x-3-2y\right)$
d) $6x^2-7x+2$
$=\left(6x^2-3x\right)+\left(-4x+2\right)$
$=3x\left(2x-1\right)-2\left(2x-1\right)$
$=\left(2x-1\right)\left(3x-2\right)$