Question

Cho x - y = -5. Tính giá trị biểu thức

B = (x - y)³ - x² + 2xy - y²

Answer 1

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

Thay x - y = -5 vào B ta có:

\(\left(-5\right)^3-\left(-5\right)^2=-125-25=-150\)

Answer 2

Ta có:

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

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

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

=\(\left(-5\right)^3-\left(-5\right)^2\) (do x-y=-5)

=\(-125-25=-150\)

Vậy...