θ is given to be in the fourth quadrant (270° < θ < 360°) for which sin(θ) < 0 and cos(θ) > 0. This means
cos²(θ) + sin²(θ) = 1 ==> sin(θ) = -√[1 - cos²(θ)] = -3/5
Now recall the double angle identity for sine:
sin(2θ) = 2 sin(θ) cos(θ)
==> sin(2θ) = 2 (-3/5) (4/5) = -24/25
