因为∠dac=180°-∠bac,∠acf=180°-∠acb,且∠cae=1/2∠dac,∠ace=1/2∠acf,
所以∠cae+∠ace=1/2∠dac+1/2∠acf=1/2[(180°-∠bac)+(180°-∠acb)]
=180°-1/2(∠bac+∠acb)
因为∠cae+∠ace+∠aec=180°,∠bac+∠acb+∠b=180°
所以180°-∠aec=180°-1/2(180°-∠b)=90°+1/2∠b
即∠aec=180°-(90°+1/2∠b)=90°-1/2∠b=90°-1/2*50°=65°
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