∵ a为锐角
所以 sin²a=1-con²a=1-(3/5)²,sina=4/5
则 tana=sina/cona=4/3
tan(a-B)=(tana-tanB)/(1+tanatanB)=(4/3-tanB)/(1+4/3tanB)=1/3
4-3tanB=1+4/3tanB
tanB=9/13
∵ a为锐角
所以 sin²a=1-con²a=1-(3/5)²,sina=4/5
则 tana=sina/cona=4/3
tan(a-B)=(tana-tanB)/(1+tanatanB)=(4/3-tanB)/(1+4/3tanB)=1/3
4-3tanB=1+4/3tanB
tanB=9/13