\(a,x^2+2xy+y^2-z^2\)
\(=\left(x+y\right)^2-z^2\)
\(=\left(x+y-z\right)\left(x+y+z\right)\)
\(b,x^3-3x^2+3x-1-8y^3\)
\(=\left(x-1\right)^3-8y^3\)
\(=\left(x-1-2y\right)\left(\left(x-1\right)^2+\left(x-1\right)2y+4y^2\right)\)
\(=\left(x-1-2y\right)\left(x^2-2x+1+2xy-2y+4y^2\right)\)
\(c,x^4+3x^3-9x-9\)
\(=\left(x^2-3\right)\left(x^2+3\right)+3x\left(x^2-3\right)\)
\(=\left(x^2-3\right)\left(x^2+3+3x\right)\)
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