Question

How do you find the standard notation of `5(cos 210+isin210)`?

Answer 1

I suppose you want this complex number in the `a+ib` form.

You have only to evaluate your `cos` and `sin` and do the nultiplication by 5:

`5[cos(210°)+isin(210°)]=`
`=5cos(210°)+5isin(210°)=`
`=5(-sqrt(3)/2)+5i(-1/2)=`
`=-5sqrt(3)/2-5/2i`

Which is in the form: `a+ib`

If you want you can evaluate the square root and the divisions but I would leave it like it is.

hope it helps