# How do you multiply  (4-8i)(3+9i)  in trigonometric form?

$\left(4 - 8 i\right) \left(3 + 9 i\right) = 12 + 36 i - 24 i - 72 {i}^{2}$
=$12 + 12 i - \left(- 72\right)$ because ${i}^{2} = - 1$
=$84 + 12 i$