Question

Cho x + y = 5. Tính A = x^2 + 2xy + y^2 - 8x - 8y + 2.

Answer 1

\(A=\left(x+y\right)^2-8\left(x+y\right)+16-14\\ A=\left(x+y-4\right)^2-14\\ A=\left(5-4\right)^2-14=-13\)

Answer 2

\(A=x^2+2xy+y^2-8x-8y+2\)

\(=\left(x+y\right)^2-8\left(x+y\right)+2\)

\(=5^2-8.5+2\)

\(=-13\)

Vậy \(A=-13\) khi x + y = 5