Найдите sina/2? tckb tga=15/8,180 град

Решение:

на интрвале (180; 270) sina<0 cosa<0

tga=2tga/2 / (1-tg^2a/2)

tga/2=y

15y^2+16y-15=0

y=-5/3

y=3/5

sina/2/cosa/2=3/5

sina/2=x

x^2=0,36-0,36x^2

x^2=0,36/1,36

sina/2=0,6/sqrt (1,36) = 0,6/0,2sqrt (34) = 3/sqrt (34)

x^2=25/9 * (1-x^2)

9x^2=25-25x^2

34x^2=25

sina/2=5/sqrt (34)