Question

AD、BC相交于O,AB∥CD,OA=OB,求证 角C=角D

Answer 1

1.AB∥CD

∠D=∠A

∠B=∠C

OA=OB

∠B=∠A

∠C=∠D

2.

∠ADB=∠ADC=90°

AB=AC

△ADB≌△ADC

CD=BD=5

BC=10