Найдите tg(a+b), если tga=3/4, cosb=3/5, 0

Tg (a + b) = (tga + tgb)/(1 - tga · tgb)
tga = 3/4
sinb = √(1 - cos²b) = √(1 - 9/25) = √ 16/25 = 4/5
tgb = sinb/cosb = 4/5 : 3/5 = 4/3
tg (a + b) = (3/4 + 4/3)/(1 - 3/4 · 4/3) = 25/12 : 0  = ∞
ответ: tg (a + b) = ∞