a) Sửa đề: \(x^2+7y-y^2+7x\)
\(=\left(x-y\right)\left(x+y\right)+7\left(x+y\right)\)
\(=\left(x+y\right)\left(x-y+7\right)\)
b) Ta có: \(2x-30y^2x-3y+20x^2y\)
\(=2x\left(1+10xy\right)-3y\left(1+10yx\right)\)
\(=\left(1+10xy\right)\left(2x-3y\right)\)
c) Ta có: \(5x^3-5x^2y-10x^2+10xy\)
\(=5x\left(x^2-xy-2x+2y\right)\)
\(=5x\left[x\left(x-y\right)-2\left(x-y\right)\right]\)
\(=5x\left(x-y\right)\left(x-2\right)\)
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