Question

7. Simplify the following product of complex numbers.
(-1 + 5i) · (4 – 8i)

Answer 1

(a+bi)(c+di) = (ac-bd) +(bc+ad)i

Answer 2

(-1*4-5*8)+(5*8+-1*4)i

Answer 3

mind the negatives (-8)

Answer 4

36 + 28i

http://www.wolframalpha.com/input/?i=%28-1+%2B+5i%29%284+%E2%80%93+8i%29%3D

Answer 5

so would it look like this
(-1 + 5i)(4 - 8i)
= -4 + 8i + 20i - 40i^2
= -4 + 28i + 40
= 36 + 28i

Answer 6

yeah straight foil works perfect