Week 2 Question 20

[punctualmoose]

I found the length of chord BD, but I couldn't see any way to prove that it's equal to chord DC. When I checked the explanation, it claimed that PAB is similar to PCD and DAB is similar to DBP. I also couldn't find an explanation to prove that either. Why are these triangles similar?

[JoyfulSapling]

@punctualmoose PAB is similar to PCD because

1. They both share angle P.
2. They share two sides, therefore angle PAB = angle PCD and angle PBA = angle PDC.