Question

Cho x + y = 3. Tính GTBT :

\(A=x^2+2xy+y^2-4x-4y+1\)

Answer 1

\(A=\left(x+y\right)^2-4\left(x+y\right)+1=3^2+4.3+1=22\)

Answer 2

\(A=x^2+2xy+y^2-4x-4y+1\)

\(A=\left(x^2+2xy+y^2\right)-4.\left(x+y\right)+1\)

\(A=\left(x+y\right)^2-4.\left(x+y\right)+1\)

Ta có: \(x+y=3\)

\(\Rightarrow A=3^2-4.3+1\)

\(A=9-12+1\)

\(A=-2\)

Vậy \(A=-2\)tại \(x+y=3\)

Tham khảo nhé~

Answer 3

A = x² + 2xy + y² - 4x - 4y + 1

A = (x+y)² - 4.(x+y) + 1

thay x + y = 3 vao A

co: A = (3)² - 4.3 + 1

A = 9 - 12 + 1

A = -2