Question

How do you simplify `(2 + 5i)(4 - i)`?

Answer 1

`13 + 18i`

Explanation:

Foil the brackets, so we end up with:

`2*4 - 2*i + 5i*4 + 5i*(-i)`

Remember that `i^2 = -1`

so we have:

`8 - 2i + 20i - 5i^2 = 13 +18i`