a)\(VT=\left(x-1\right)\left(x^2+x+1\right)\)
\(=x^2\left(x-1\right)+x\left(x-1\right)+\left(x-1\right)\)
\(=x^3-x^2+x^2-x+x-1\)
\(=x^3-1=VP\)
b)\(VT=\left(x^3+x^2y+xy^2+y^3\right)\left(x-y\right)\)
\(=x^3\left(x-y\right)+x^2y\left(x-y\right)+xy^2\left(x-y\right)+y^3\left(x-y\right)\)
\(=x^4-x^3y+x^3y-x^2y^2+x^2y^2-xy^3+xy^3-y^4\)
\(=x^4-y^4\)
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a) VT= x( x²+x+1) - 1( x²+x+1)
= x³+x²+x- x²-x-1
= x³-1
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