Question

what is 5cis(π) in rectangular form?

Answer 1

cis ?

Answer 2

Its a complex numbers question.
cis(a) = cos(a) +isin(a)
so 5cis(pi) = 5(cos(pi)+isin(pi))
=-5 However this solution looked at bit dodgy so I want someone to confirm that its correct.

Answer 3

\[\Large\rm 5cis(\pi)=5\left[\cos(\pi)+\mathcal i \sin(\pi)\right]\]\[\Large\rm 5cis(\pi)=5\left[-1+\mathcal i(0)\right]\]\[\Large\rm 5cis(\pi)=-5+0\mathcal i\]Seems right, yah? :)

Answer 4

He is right.

Answer 5

Cool thanks for the replies!