(1)因为
sin(a-b)=sin(a)*cos(b)-cos(a)*sin(b)=1/3
sin(a+b)=sin(a)*cos(b)+cos(a)*sin(b)=1/2
3sin(a)*cos(b)-3cos(a)*sin(b)=1
2sin(a)*cos(b)+2cos(a)*sin(b)=1
3sin(a)*cos(b)-3cos(a)*sin(b)=2sin(a)*cos(b)+2cos(a)*sin(b)
所以解得sinacosb=5cosasinb
(2)因为tana=5tanb
原试可以换成sina/cosa=5sinb/cosb
对掉一下位置,就同证明第一题一样啦