Question

How do you find the complex roots of `a^2-81=0`?

Answer 1

This quadratic has only two Real roots.

Explanation:

This can be factored as a difference of squares, or `a^2-b^2=0`.

`a^2-81=0`

`a^2-9^2=0`

`(a+9)(a-9)=0`

So the two solutions, both of which are Real, are `a=+-9`.