ĐKXĐ: \(x\ne\pm y\)
\(\dfrac{x+y}{x^3-y^3}\cdot C=\dfrac{3x^2+3xy}{x^2+xy+y^2}\)
=>\(C=\dfrac{3x^2+3xy}{x^2+xy+y^2}:\dfrac{x+y}{x^3-y^3}\)
=>\(C=\dfrac{3x\left(x+y\right)}{x^2+xy+y^2}\cdot\dfrac{\left(x-y\right)\left(x^2+xy+y^2\right)}{x+y}\)
=>C=3x(x-y)=3x2-3xy