Question

在四边形ABCD中,∠A=∠C,∠ABC=∠ADC,求DC//AB

Answer 1

内角和=∠A+∠C+∠ABC+∠ADC=360

而∠A=∠C,∠ABC=∠ADC

所以,∠A+∠A+∠ABC+∠ABC=360

2(∠A+∠ABC)=360

∠A+∠ABC=180

DC//AB