i understand the first and 3rd now

and i figured out the word problem by finding the explaining to find the midpoints that cross the requested sides.

but the second one is still roaming around in my head...

how did you get from

$\displaystyle

\tan^{-1}(-1)

$

to

$\displaystyle

\tan^{-1}(-1)=\tfrac{3}{4}\pi, \ \tfrac{7}{4}\pi, \ \tfrac{11}{4}\pi, \ \tfrac{15}{4}\pi, \ ...

$

i've remember vaguely doing something similar to this, however, it's just not coming back to me.

Thanks for the help on the others