Bài 7:
a:Sửa đề: 2x(x-2)-3y(x-2)
Ta có: 2x(x-2)-3y(x-2)
\(=\left(x-2\right)\cdot2x-\left(x-2\right)\cdot3y\)
=(x-2)(2x-3y)
b: 20a(x+y)-5c(x+y)
=(x+y)(20a-5c)
=5(4a-c)(x+y)
c: 12x(x+5)-2y(x+5)
=(x+5)(12x-2y)
=2(6x-y)(x+5)
d: 2a(x-1)+b(x-1)-(x-1)
=(x-1)(2a+b-1)
Bài 8:
a: \(3x^3\left(x+2\right)-15x\left(2y-3z\right)^3\)
\(=3x\cdot x^2\left(x+2\right)-3x\cdot5\cdot\left(2y-3z\right)^3\)
\(=3x\left\lbrack x^2\left(x+2\right)-5\left(2y-3z\right)^3\right\rbrack\)
b: \(\left(x+1\right)^3-4\left(x+1\right)\)
\(=\left(x+1\right)\left\lbrack\left(x+1\right)^2-4\right\rbrack\)
=(x+1)(x+1+2)(x+1-2)
=(x+1)(x+3)(x-1)
c: \(9x^2\left(y+z\right)+6\left(y+z\right)^2\)
\(=3\left(y+z\right)\cdot3x^2+3\left(y+z\right)\cdot2\left(y+z\right)\)
\(=3\left(y+z\right)\left(3x^2+2y+2z\right)\)
d: \(2x\left(x-2\right)-8\left(x-2\right)^2\)
\(=2\left(x-2\right)\left\lbrack x-4\left(x-2\right)\right\rbrack\)
=2(x-2)(x-4x+8)
=2*(x-2)(-3x+8)
bài 6:
a: \(18x^2y-12x^3=6x^2\cdot3y-6x^2\cdot2x=6x^2\left(3y-2x\right)\)
b: \(x^{m+3}-2\cdot x^{m+1}\)
\(=x^{m+1}\cdot x^2-2\cdot x^{m+1}\)
\(=x^{m+1}\left(x^2-2\right)\)
c: \(3x^2y-6xy^2z=3xy\cdot x-3xy\cdot2yz=3xy\left(x-2yz\right)\)
d: \(5x^{m+3}+10x^3=5x^3\cdot x^{m}+5x^3\cdot2=5x^3\left(x^{m}+2\right)\)
