x3 + 6x2 + 9x
= x3 + 3x2 + 3x2 + 9x
= x2(x + 3) + 3x(x + 3)
= (x2 + 3x)(x + 3)
= x(x + 3)(x + 3)
= x(x + 3)2
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a: \(x^3+6x^2+9x\)
\(=x\left(x^2+6x+9\right)\)
\(=x\left(x+3\right)^2\)
b: \(x^2-2xy+y^2-\left(x-y\right)\left(3y-x\right)\)
\(=\left(x-y\right)^2+\left(x-y\right)\left(x-3y\right)\)
\(=\left(x-y\right)\left(x-y+x-3y\right)\)
\(=2\left(x-y\right)\left(x-2y\right)\)
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