Question

How do you simplify `(2i-1)(2i+1)`?

Answer 1

-5

Explanation:

This should be known thing, well before learning about complex numbers:

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

`(2i-1)(2i+1)=(2i)^2-1 =-4-1=-5`