Question

How do you factor `0.09y^2 - 0.81`?

Answer 1

`0.09y^2 - 0.81 = (0.3y+0.9)(0.3y-0.9)`

Explanation:

The difference of squares formula gives us
`a^2 - b^2 = (a+b)(a-b)`
(you can multiply this out to confirm)

`0.09y^2 = (0.3y)^2`
and
`0.81 = 0.9^2`

Thus, by the difference of squares formula

`0.09y^2 - 0.81 = (0.3y+0.9)(0.3y-0.9)`