Question

这道题怎么做啊，各位学霸帮帮忙呗。谢谢啦

Answer 1

∠BEC=180°-∠ABC-∠ECB=180°-∠ABC-∠ACB/2
∠A=180°-∠ABC-∠ACB
∴∠BEC -∠A/2=180°-∠ABC-∠ACB/2-(180°-∠ABC-∠ACB)/2
=180°-∠ABC-∠ACB/2-90°+∠ABC/2+∠ACB/2
=90°-∠ABC/2=90°-∠FBO=∠BOF

Answer 2

因为90°=∠BOF+∠FBO和180°=∠A+∠B+∠C=∠A+2∠FBO+∠C可得出
∠FBO=(1/2)∠A+(1/2)∠C=∠A+(1/2)∠C-(1/2)∠A

又因为∠BEC=∠A+(1/2)∠C 带入上式就可的原式

Answer 3

初中的

追问

嗯

Answer 4