∴∠B=5/6∠C

∴∠A+∠B=2∠C= 180

∴∠C=90

△ ABC is a right triangle.

2 questions without pictures

3. Relationship: ∠ α+∠ β = ∠ b.

Prove AB parallel CD in quadrilateral ABCD

∴∠B+∠C= 180

∵∠ α +∠+β = 180.

∴∠α+∠β= 180-∠C=∠B

∴∠α+∠β=∠B

4. Relationship: ∠PAB+∠PDC=∠APD

It is proved that the parallel line with point P as CD intersects with point F, ∴AB‖CD‖FP.

∴∠PAB=∠APF,∠PDC=∠DPF

∴∠APF+∠DPF=∠PAB+∠PDC=∠APD