Question

find the exact value of sin tetha/2, Cos tetha = -4/5, tetha is in qudrant 3

Answer 1

use half angle identity
\[\sin (\theta/2) = \sqrt{\frac{1-\cos \theta}{2}}\]
since theta is in quad 3, sin(theta/2) will be positive

Answer 2

But how do you find the value?

Answer 3

plug in value for cos(theta)