Question

Cho x-y=7.Tính:

1)A=x(x+2)+y(y-2)-2xy+37

2)\(B=x^2\left(x+1\right)-y^2\left(y-1\right)+xy-3xy\left(x-y+1\right)-9^5\)

Answer 1

\(A=x\left(x+2\right)+y\left(y-2\right)-2xy+37\)

\(A=x^2+2x+y^2-2y-2xy+37\)

\(A=\left(x^2+y^2-2xy+1+2x-2y\right)+36\)

\(A=\left(x-y+1\right)^2+36\)

\(A=\left(7+1\right)^2+36\)

\(A=8^2+36\)

\(A=100\)

Answer 2

\(B=x^2\left(x+1\right)-y^2\left(y-1\right)+xy-3xy\left(x-y+1\right)-95\) \((9^5\) \(sai\)\()\)

\(B=x^3+x^2-y^3+y^2+xy-3x^2y+3xy^2-3xy-95\)

\(B=\left(x^3-3x^2y+3xy^2-y^3\right)+\left(x^2+xy-3xy+y^2\right)-95\)

\(B=\left(x-y\right)^3+\left(x^2-2xy+y^2\right)-95\)

\(B=\left(x-y\right)^3+\left(x-y\right)^2-95\)

\(B=7^3+7^2-95\)

\(B=297\)