Question

4x^2-9=0

Answer 1

\(\large\color{black}{ 4x^2 = (2x)^2 }\)
\(\large\color{black}{ 9 = (3)^2 }\)

and we have a rule, \(\large\color{blue}{ a^2-b^2=(a-b)(a+b) }\) so aply this rule to your equation.