Question

Find the product:
(2x² − 5y²) × (x² + 3y²)

Answer 1

By horizontal method:

$$\begin{gathered} (2x^2-5y^2)\times (x^2+3y^2) \\ =2x^2(x^2+3y^2)-5y^2(x^2+3y^2) \\ =2x^4+6x^2{y}^2-5x^2{y}^2-15y^4 \\ =2x^4+x^2{y}^2-15y^4 \end{gathered}$$