Gievn that tan A =3 and sin (A-B)=2 cos (A+B) , find tan B

i got tan B=-1/5

Find general solution , in rad cos b + cos 3b +cos 5b =0

cos b + 2 cos 4b cos b =0

cos b (1+2cos 4b )=0

cos b =0

and cos b = -1/2

I can only reach this far , i am not sure about the general solution >

Deduce

no idea bout this .