exact value Find the value of sinx/2 if sinx=1/4 and x is such that pi/2 Solution sin x =1/4. cos x = sqrt (1 - (sin x)^2) => -(sqrt 15) / 4 In the interval pi/2< x < pi sin (x/2) = sqrt ((1 - cos x)/2) => sin (x/2) = sqrt[(4 - sqrt 15)/8] The required value of sin (x/2) = sqrt[(4 - sqrt 15)/8].