Question

How do you simplify `(-7i)(-3i)(-5-i)`?

Answer 1

`-105i^2-21i^3`

Explanation:

first multiply two of the terms*
`(-7i)(-3i)`

you now have
`21i²`

now multiply that with `(-5-i)`
`21i^2` `(-5-i)`

you get
`-105i^2-21i^3`

*you can chose any two but these are easier

Answer 2

`105+21i`

Explanation:

Begin by multiplying the 2 leading terms.

`(-7i)(-3i)=21i^2=-21`

`color(orange)"Reminder " color(red)(bar(ul(|color(white)(a/a)color(black)(i^2=(sqrt(-1))^2=-1)color(white)(a/a)|)))`

The original question can now be expressed as.

`-21(-5-i)=105+21i`