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Bài 4:
a: \(=7xy\left(2-3-4\right)=-35xy\)
b: \(=\left(x-5\right)\left(x+y\right)\)
c: \(=10x\left(x-y\right)+8\left(x-y\right)=2\left(x-y\right)\left(5x+4\right)\)
d: \(=\left(x+y\right)^3-\left(x+y\right)\)
=(x+y)(x+y+1)(x+y-1)
e: =x^2+8x-x-8
=(x+8)(x-1)
f: \(=2x^2-4x+x-2=\left(x-2\right)\left(2x+1\right)\)
g: =-5x^2+15x+x-3
=(x-3)(-5x+1)
h: =x^2-3xy+xy-3y^2
=x(x-3y)+y(x-3y)
=(x-3y)*(x+y)
Bài 4:
a: \(=7xy\left(2-3-4\right)=-35xy\)
b: \(=\left(x-5\right)\left(x+y\right)\)
c: \(=10x\left(x-y\right)+8\left(x-y\right)=2\left(x-y\right)\left(5x+4\right)\)
d: \(=\left(x+y\right)^3-\left(x+y\right)\)
=(x+y)(x+y+1)(x+y-1)
e: =x^2+8x-x-8
=(x+8)(x-1)
f: \(=2x^2-4x+x-2=\left(x-2\right)\left(2x+1\right)\)
g: =-5x^2+15x+x-3
=(x-3)(-5x+1)
h: =x^2-3xy+xy-3y^2
=x(x-3y)+y(x-3y)
=(x-3y)*(x+y)
\(x^2y-y+xy^2-x\)
=> \(x\left(xy-1\right)+y\left(-1+xy\right)\)
=> \(\left(-1+xy\right)\left(x+y\right)\)
a,\(x^2\)- xy - 8x + 8y
= \(\left(x^2-8x\right)\)- (xy - 8y)
= x( x - 8 ) - y( x - 8)
= (x - y)(x - 8)
\(9-4x^2-4xy-y^2\)
⇔ \(3^2-\left[\left(2x\right)^2+2.2x.y+y^2\right]\)
⇔\(3^2-\left(2x+y\right)^2\)
⇔\(\left(3-2x+y\right)\left(3+2x+y\right)\)
\(9-4x^2-4xy-y^2\)
=> \(9-\left(2x+y\right)\left(2x+y\right)\)
=> \(-\left(2x+y+3\right)\left(2x+y+3\right)\)
\(x^3-2x^2+x-xy\)
\(=x\left(x^2-2x+1-y^2\right)\)
\(=x\left[\left(x^2+2x+1\right)-y^2\right]\)
\(=x\left[\left(x-1\right)^2-y^2\right]\)
\(=x\left(x-1-y\right)\left(x-1+y\right)\)
\(\frac{x^2-y^2+6x+9}{x+y+3}=\frac{\left(x+3\right)^2-y^2}{x+y+3}=\frac{\left(x+3-y\right)\left(x+3+y\right)}{x+y+3}=x-y+3\)