The Attempt at a Solution
I substitute into (sin x)^2 and get an answer of -2 but the answer should be 2 . how to i do this question.
but ((sin x)^2 )^0.5 gives us two answers
sinx and -sinx
yeah, generally it does, but look here we are only integrating in [-pi.0], and obviously sinx, where x is from [-pi,0] is always negative, so
I sin(x) I = -sinx, whenever x is from the interval [-pi. 0]
now as halls said, integrating this you will get the desired answer.