sin(a+b)=2/3
sinacosb+cosasinb=2/3 (1)
sin(a-b)=3/4
sinacosb-cosasinb=3/4 (2)
(1)+(2),2sinacosb=17/12
(1)-(2),2cosasinb=-1/12
tana/tanb =2sinacosb/2cosasinb=-17
sin(a+b)=2/3
sinacosb+cosasinb=2/3 (1)
sin(a-b)=3/4
sinacosb-cosasinb=3/4 (2)
(1)+(2),2sinacosb=17/12
(1)-(2),2cosasinb=-1/12
tana/tanb =2sinacosb/2cosasinb=-17