7:
a: \(\left(x^2-2x+1\right)\left(x-1\right)\)
\(=x^3-x^2-2x^2+2x+x-1\)
\(=x^3-3x^2+3x-1\)
b: \(\left(x^3-2x^2+x-1\right)\left(5-x\right)\)
\(=5x^3-x^4-10x^2+2x^3+5x-x^2-5+x\)
\(=-x^4+7x^3-11x^2+6x-5\)
=>\(\left(x^3-2x^2+x-1\right)\left(x-5\right)=-\left(-x^4+7x^3-11x^2+6x-5\right)\)
\(=x^4-7x^3+11x^2-6x+5\)
Bài 8:
a: \(\left(x^2y^2-\frac12xy+2y\right)\left(x-2y\right)\)
\(=x^3y^2-2x^2y^3-\frac12x^2y+xy^2+2xy-4y^2\)
b: \(\left(x^2-xy+y^2\right)\left(x+y\right)=x^3+x^2y-x^2y-xy^2+xy^2+y^3\)
\(=x^3+y^3\)
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