PC=PD=PE,
Points c, d and e are three * * * circles with p as the center.
From the angle of circle theorem: ∠ DPE = 2 ∠ ECD = 2y.
∠BDP=90,∠BEP=90
∴∠B+∠DPE= 180
∠B= 180 -2y
( 180 ? 2y ) / 360 * 2πR =πR(90? y )/90