Question

[Huynh Le Thien Tri]

Cho x=y+5 tính giá trị biểu thức x(x+2)+y(y-2)-2xy+64

Answer 1

[Trà My]

\(x\left(x+2\right)+y\left(y-2\right)-2xy+64=x^2+2x+y^2-2y-2xy+64\)

\(=\left(x^2-2xy+y^2\right)+\left(2x-2y\right)+64\)\(=\left(x-y\right)^2+2\left(x-y\right)+64\)

\(=\left(x-y\right)\left(x-y+2\right)+64\)\(=\left(y+5-y\right)\left(y+5-y+2\right)+64\)

=5.7+64=99=99