I have a question about polygons. Here's how it goes:
I know that the sum of interior angles of the regular nonagon is 180º(n-2)=
= 180(9) -360
So each of the interior angle is 1260º/9 = 140º
angle PCD + angle BCD = 180º (adjacent angles on a straight line)
angle PCD = 180º - 140º
angle PCD = 40º
So that explains part a).
Can you please give me tips on part b)?