Question

How to factor 81y^2 -4

Answer 1

`\bf \textit{difference of squares} \\ \quad \\ (a-b)(a+b) = a^2-b^2\qquad \qquad a^2-b^2 = (a-b)(a+b)\\\\ -------------------------------\\\\ 81y^2-4\quad \begin{cases} 81=9^2\\ 4=2^2 \end{cases}\implies 9^2y^2-2^2\implies (9y)^2-2^2 \\\\\\ (9y-2)(9y+2)`