Question

How do you multiply `(7-3i)(7+3i)`?

Answer 1

`58`

Explanation:

Note that for any `a, b` the difference of squares identity holds:

`a^2-b^2 = (a-b)(a+b)`

So we find:

`(7-3i)(7+3i) = 7^2-(3i)^2 = 49-9i^2 = 49+9 = 58`