证明∵ab=ac
cd⊥ab于d,be⊥ac于e
∠adc=∠aeb=90
∠dac=∠ead
∴△adc全等△aeb
∴ad=ae
∠adc=∠aeb=90
af=af
∴△adf全等△aef
∠baf=∠caf