a/ \(x^2-2x-15\)
\(=x^2+3x-5x-15\)
\(=x\left(x+3\right)-5\left(x+3\right)\)
\(=\left(x+3\right)\left(x-5\right)\)
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b/ \(y\left(x-z\right)+7\left(z-x\right)\)
\(=y\left(x-z\right)-7\left(x-z\right)\)
\(=\left(x-z\right)\left(y-7\right)\)
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c/ \(27x^2\left(y-1\right)-9x^3\left(1-y\right)\)
\(=27x^2\left(y-1\right)+9x^3\left(y-1\right)\)
\(=9x^2\left(y-1\right)\left(x+3\right)\)
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