a: \(P=2x^3-x\left(3+x^2\right)-x\left(x^2-x-3\right)\)
\(=2x^3-3x-x^3-x^3+x^2+3x\)
\(=x^2\)
Khi x=10 thì \(P=10^2=100\)
b: \(Q=x^2\left(x-y+y^2\right)-x\left(xy^2+x^2-xy-y\right)\)
\(=x^3-x^2y+x^2y^2-x^2y^2-x^3+x^2y+xy\)
=xy
KHi x=5 và y=20 thì \(Q=5\cdot20=100\)