Question

Cho x + y = 7. Tính giá trị biểu thức sau:

A = (x+y)³+2x²+4xy+2y²

Answer 1

A = ( x + y )³ + 2x² + 4xy + 2y²
A = 5³ + 2 ( x² + 2xy + y² )
A = 125 + 2 ( x + y )²
A = 125 + 2 . 5²
A = 125 + 2 . 25
A = 125 + 50 = 175

Answer 2

\(A=\left(x+y\right)^3+2x^2+4xy+2y^2\)

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

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

\(=7^3+2\cdot7^2=441\)