Question

Answer 1

Câu 4:

\(M=\left(\dfrac{\left(x^2-xy+y^2\right)\left(x+y\right)-\left(x-y\right)\left(x^2+xy+y^2\right)}{\left(x-y\right)\left(x+y\right)}\right):\dfrac{x^2-y^2-x^2}{x-y}\)

\(=\dfrac{x^3+y^3-x^3+y^3}{\left(x-y\right)\left(x+y\right)}\cdot\dfrac{x-y}{-y^2}\)

\(=\dfrac{-2y^3}{\left(x+y\right)\cdot y^2}=\dfrac{-2y}{x+y}\)

b: Khi x=2y thì \(M=\dfrac{-2y}{2y+y}=\dfrac{-2y}{3y}=\dfrac{-2}{3}\)