Question

I just don't understand the geometry behind this! How is theta 1 in red equal to theta 1 in black? And same with theta 2? I need to figure out the angles to solve the rest of my problem, but I am already stuck in figuring out how these angles are the same. Please help asap.

img809.imageshack.us/img809/6872/picture2ju.png

Answer 1

Looks like they are doing some kind of rotation.

Here is an easier way:

from red B1 draw a perpendicular to the x-axis to get a right-angled triangle.
So the angle at red B1 is black Ø2

since in the original Ø1+Ø2=90
and in the new triangle the angle at P must be Ø1