Question

Factorise:
20x² – 45

Answer 1

$$\begin{gathered} 20x^2-45 \\ =5\left(4x^2-9\right) \\ =5\left[{\left(2x\right)}^2-3^2\right] \\ =5\left(2x+3\right)\left(2x-3\right)\left[a^2-b^2=\left(a+b\right)\left(a-b\right)\right] \end{gathered}$$