Factor 4a^2-36a+81

$4 a^{2} - 36 a + 81$

Step 1

Rewrite $4 a^{2}$ as ${(2 a)}^{2}$ .

${(2 a)}^{2} - 36 a + 81$

Step 2

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

${(2 a)}^{2} - 36 a + 9^{2}$

Step 3

Check that the middle term is two times the product of the numbers being squared in the first term and third term.

$36 a = 2 \cdot (2 a) \cdot 9$

Step 4

Rewrite the polynomial.

${(2 a)}^{2} - 2 \cdot (2 a) \cdot 9 + 9^{2}$

Step 5

Factor using the perfect square trinomial rule $a^{2} - 2 a b + b^{2} = {(a - b)}^{2}$ , where $a = 2 a$ and $b = 9$ .

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