Question

Rewrite −1 + 2i in polar form.

Answer 1

The length of the radius would sqrt(1+4), or sqrt(5).
                                                                                           2
The angle would be in Quadrant II and would be arctan ------ , or arctan (-2).
                                                                                           -1

Find this angle using a calculator or table.

Then you end up with -1+2i = sqrt(5) angle arctan(-2).  The angle would be + and measured from the + horizontal axis.