Question

Find the product:

(3x² + 5x − 9)(3x −9)

Answer 1

By column method:

$$\begin{gathered} 3{\mathrm{x}}^2+5\mathrm{x}-9 \\ \underline{\times (3\mathrm{x}-9)} \\ 9{\mathrm{x}}^3+15{\mathrm{x}}^2-27\mathrm{x} \\ \underline{-27{\mathrm{x}}^2-45\mathrm{x}+81} \\ \mathrm{Add}:9{\mathrm{x}}^3-12{\mathrm{x}}^2-72\mathrm{x}+81 \\ \therefore (3{\mathrm{x}}^2+5\mathrm{x}-9)(3\mathrm{x}-9)=9{\mathrm{x}}^3-12{\mathrm{x}}^2-72\mathrm{x}+81 \end{gathered}$$