Question

求11 12题.最好有解题思路.

Answer 1

cos a+b=cosacosb-sinasinb=1/3, cos a-b=cosacosb+sinasinb=1/5.

联立方程式得cosacob=4/15,sinasinb=(-1/15);tanatanb=sinasinb/cosacosb=(-1/4)