Зная, что sint=4/5, п/2

Tg (π/4 + а) = (tgπ/4 + tga) / (1 - π/4*tga) = (1 + tga) / (1 - tga)

tga = Sina/Cosa

Cos^ a = 1 - 16/25 = 9/25, Cos a = - 3/5

tga = 4/5: (-3/5) = - 4/3

tg (π/4 + а) = (1 + tga) / (1 - tga) = (1 - 4/3) / (1 + 4/3) = - 1/3 / 7/3 = - 1/7