Precalculus Examples

$81 y^{2} - 4$

Step 1

Rewrite $81 y^{2}$ as ${(9 y)}^{2}$ .

${(9 y)}^{2} - 4$

Step 2

Rewrite $4$ as $2^{2}$ .

${(9 y)}^{2} - 2^{2}$

Step 3

Since both terms are perfect squares, factor using the difference of squares formula, $a^{2} - b^{2} = (a + b) (a - b)$ where $a = 9 y$ and $b = 2$ .

$(9 y + 2) (9 y - 2)$