Question

How do you multiply `(15+ 13i ) ( 12- 9i )`, assuming `i` is an imaginary number?

Answer 1

`297+21i`

Explanation:

You multiply them just like real numbers, assuming that `i *i =-1`

`(15+13i)(12-9i)`

`=15*12+13i*12-15*9i-13i*9i`

`=180+156i-135i+117`

`=297+21i`