sina=3/5(pai/2sina=3/5(pai/2sina=3/5(pai/2由sina=3/5可知cosa=-4/5,所以tana=-3/4由tan(pai-b)=1/2可知tanb=-1/2tan2b=2tanb/(1-tanb*tanb)=-4/3tan(a-2b)=(tana-tan2b)/(1+tana*tan2b)=7/24
sina=3/5(pai/2由sina=3/5可知cosa=-4/5,所以tana=-3/4由tan(pai-b)=1/2可知tanb=-1/2tan2b=2tanb/(1-tanb*tanb)=-4/3tan(a-2b)=(tana-tan2b)/(1+tana*tan2b)=7/24