Для начала найдем значения sin(a), sin(b), cos(a) и cos(b) по формулам:
tg(a) = sin(a)/cos(a) = 1/3
sin(a) = 1/(sqrt(1 + tg^2(a))) = 1/(sqrt(1 + 1/9)) = 3/(sqrt(10))

tg(b) = sin(b)/cos(b) = 1/2
sin(b) = 1/(sqrt(1 + tg^2(b))) = 1/(sqrt(1 + 1/4)) = 2/(sqrt(5))

Теперь подставим найденные значения в исходное выражение:
sin(a+b)/sin(a)sin(b) = (sin(a)cos(b) + sin(b)cos(a))/(sin(a)sin(b)) = [(3/(sqrt(10)) cos(b) + 2/(sqrt(5)) cos(a))]/(3/(sqrt(10)) 2/(sqrt(5)))

cos(a) = 1/sqrt(1 + tg^2(a)) = 1/sqrt(1 + 1/9) = 3/(sqrt(10))
cos(b) = 1/sqrt(1 + tg^2(b)) = 1/sqrt(1 + 1/4) = 2/(sqrt(5))

(sin(a)cos(b) + sin(b)cos(a))/(sin(a)sin(b)) = [(3/(sqrt(10)) 2/(sqrt(5)) + 2/(sqrt(5)) 3/(sqrt(10)))] / [(3/(sqrt(10)) * 2/(sqrt(5))] = (6/(10) + 6/(10))/(6/(10)) = 12/10 = 1.2

Итак, значение выражения sin(a+b)/sin(a)*sin(b) равно 1.2.