Question

How do you factor `4y ^ { 2} - 81`?

Answer 1

`(2y+9)(2y-9)`

Explanation:

`4y^2 -81 = (2y)^2 -9^2`

Recall that: `a^2-b^2 = (a+b)(a-b)`

So, in this case: `(2y)^2 -9^2 = (2y+9)(2y-9)`