\(-2x^3y^4:D=xy^2\)
\(D=\left(-2x^3y^4\right):\left(xy^2\right)\)
\(D=-2x^2y^2\)
\(\dfrac{10x^5y^2-6x^3y^4+8x^2y^5}{D}=\dfrac{10x^5y^2-6x^3y^4+8x^2y^5}{-2x^2y^2}\)
\(=\dfrac{10x^5y^2}{-2x^2y^2}+\dfrac{-6x^3y^4}{-2x^2y^2}+\dfrac{8x^2y^5}{-2x^2y^2}\)
\(=-5x^3+3xy^2-4y^3\)