Tg(a+b) если sina=12/13 cosb=3/5 a,b принадлежит первой четверти

Cos(a) = V(1 - (12/13)^2 ) = V(13^2 - 12^2) /13 = 5/13,
sin(B) = V(1 - (3/5)^2) = V(5^2 - 3^2) /5 = V(2*8) /5 = 4/5,
tg(a+B) = sin(a+B)/cos(a+B) =
= ( sin(a)*cos(B) + sin(B)*cos(a) )/( cos(a)*cos(B) - sin(a)*sin(B) ) = 
= ( (12/13)*(3/5) + (4/5)*(5/13) )/( (5/13)*(3/5) - (12/13)*(4/5) ) = 
 = ( 12*3 + 4*5 )/( 5*3 - 12*4) = (36+20)/(15 - 48) = 56/(-33) = -56/33.