Question

cho x+y=3
tính x^2 + 2xy + y^2 - 4x - 4y +10

Answer 1

\(x^2+2xy+y^2-4x-4y+10=\left(x+y\right)^2-4\left(x+y\right)+10=3^2-4.3+10=7\)

Answer 2

\(x^2+2xy+y^2-4x-4y+10\)\(=\left(x^2+2xy+y^2\right)-4x-4y+10\)

\(=\left(x+y\right)^2-\left(4x+4y-10\right)=\left(x+y\right)^2-\left[2\left(x+y\right)-10\right]\)

Thay x + y = 3 vào, ta được:

 \(3^2-\left[2\cdot3-10\right]=9-\left(-4\right)=13\)