Question

dạ day ạ

Answer 1

\(P=7x\left(x^2y-5xy^2+2y^3\right)-5y\left(x^2-3xy\right)\left(x-4y\right)\)

\(=7x^3y-35x^2y^2+14xy^3-5y\left(x^3-4x^2y-3x^2y+12xy^2\right)\)

\(=7x^3y-35x^2y^2+14xy^3-5y\left(x^3-7x^2y+12xy^2\right)\)

\(=7x^3y-35x^2y^2+14xy^3-5x^3y+35x^2y^2-60xy^3\)

\(=2x^3y-46xy^3\)

Khi x=-2;y=-1 thì \(P=2\cdot\left(-2\right)^3\cdot\left(-1\right)-46\cdot\left(-2\right)\cdot\left(-1\right)^3\)

\(=2\cdot\left(-8\right)\cdot\left(-1\right)+46\cdot2\cdot\left(-1\right)\)

=16-92

=-76