# Math Help - Writing a number in trigonometric form

1. ## Writing a number in trigonometric form

I feel dumb asking this, but I cant get the right answer...

Write in Trigonometric form

9.6-5.5i

2. I think you require

given $z = a+bi$

then

$z = \sqrt{a^2+b^2}~\text{cis}\left(\tan^{-1}\left(\frac{b}{a}\right)\right)$