Sin(a+b): если sina=3/5 ,sinb=-5/13

sin(a+b)=sina*cosb+cosa*sinb
cosa=sqrt(1-sin^2a)
cosa=sqrt(16/25)=4/5
cosb=sqrt(1-(25/169)
cosb=sqrt(144/169)=12/13
3/5*12/13+(-5/12)*4/5=36/65-1/3=(108-65)/195=43/195
Ответ: 43/195