Question

I am absolutely lost - http://prntscr.com/bgyjp2

Answer 1

So we're just multiplying?
Remember this?
\(\large\rm z_1=A cis(\theta_1)\)
\(\large\rm z_2=B cis(\theta_2)\)
then
\(\large\rm z_1\cdot z_2=A\cdot B cis(\theta_1+\theta_2)\)
You multiply the magnitudes and add the angles, ya?

Answer 2

So -

2 * 7 (cos140 + cos65)?

Answer 3

no no, cis is not cos

cis is short for cosine + i sine

Answer 4

\(\large\rm cis(140)=cos140+i sin140\)

Answer 5

It's just a shorthand notation

Answer 6

2*7(cis(140+65))

Answer 7

Mmmm good good good :)
\(\large\rm 14cis(205)=14(cos205+i sin205)\)