How do you multiply $(- 10 + 7 i) (- 9 + 2 i)$ $(-10+7i)(-9+2i)$ in trigonometric form?

Question

1463 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2016-03-05T19:53:54

$90 - 20 i - 63 i + 14 i^{2} \to 90 - 83 i - 14 = 76 - 83 i$ $90-20i-63i+14i^2 ->90-83i-14=76-83i$

Foil it out and the collect like terms. Note that $i^{2} = - 1$ $i^2 = -1$ so I substitute it in and simplify.

How do you multiply (−10+7i)(−9+2i) (-10+7i)(-9+2i) in trigonometric form?