sin(a+b)=sinacosb+cosasinb=1/2
sin(a-b)=sinacosb-cosasinb=1/3
所以sinacosb=(1/2+1/3)/2=5/12
cosasinb=(1/2-1/3)/2=1/12
相除
sinacosb/cosasinb=5
(sina/cosa)/(sinb/cosb)=5
tana/tanb=5
所以tana=5tanb