Question

如图,5个同样大小的三角形拼成一个长方形,求∠ABC+∠ADC+∠ACB的度数

Answer 1

∠ACB=45°

tan∠ABC=1/3

tan∠ADC=1/2

tan(∠ABC+∠ADC)=(1/3+1/2)/(1-1/2*1/3)

=1

所以∠ABC+∠ADC=45°

所以∠ABC+∠ADC+∠ACB=90°