Basic Math Examples

$25 r^{2} - 81$

Step 1

Rewrite $25 r^{2}$ as ${(5 r)}^{2}$ .

${(5 r)}^{2} - 81$

Step 2

Rewrite $81$ as $9^{2}$ .

${(5 r)}^{2} - 9^{2}$

Step 3

Since both terms are perfect squares, factor using the difference of squares formula, $a^{2} - b^{2} = (a + b) (a - b)$ where $a = 5 r$ and $b = 9$ .

$(5 r + 9) (5 r - 9)$