\(-10x^3y\left(\frac{2}{5}x^2y+\frac{3}{10}xy^2\right)+3x^4y^3\)
\(=-4x^5y^2-3x^4y^3+3x^4y^3=-4x^5y^2\)
\(-10x^3y\left(\frac{2}{5}x^2y+\frac{3}{10}xy^2\right)+3x^4y^3\)
\(=\left[\left(-10x^2\right)\left(y\right)\right].\left[\left(\frac{2}{5}x^2\right)\left(y\right)+\left(\frac{3}{10}x\right)\left(y^2\right)\right]+3x^4y^3\)
\(=-4x^5y^2-3x^4y^3+3x^4y^3\)
\(=-4x^5y^2\)