Originally Posted by

**lila_sine** :)THANKS ticbol for all your help and yes, I did a typo.

:)THANKS earboth also for the diagram!

However, ticbol with:

I really do not understand how you got 90 degrees.

Well I looked at the problem again with the definition (thanks!:)) and I created a few more lines such as XY, C1Y and C2Y. Then from that since they were all isosceles triangles, I named angles A, B C and D. As the sum of a triangle is 180, A+B+C+D = 180. Maybe that was practically the same thing you were saying...except more mathematically but I just want to check if that proof is viable.

Sorry for troubling you!