A small portion of the last chapter in my textbook is devoted to cis problems. It is very unclear about the cis trigometric function, providing no examples whatsoever.

Here are two problems from my textbook I attempted to work on:

"Write in a + bi form: $\displaystyle 5 cis 300°$

Round the value of a to the hundredth.

Leave your answer in the form ___+___

**i**"

and

"Multiply: $\displaystyle (6 cis 100°) (2 cis 70°)$

Leave your answer in the form ___cis___°"

If I could get an explanation on these two problems, I'll (hoprefully

) be able to work though the rest, and I'll have a good study session. I'm guaranteed at least one question on cis on my final.

At first I thought the folks who wrote the book made a typo for cos, given the "I" key on the keyboard is so close to the "O" key.

Many thanks in advance to quick help!