If 90∘<x<180∘, which of the following statements about sin2x is correct?
(a) sin2x is positive because 2x remains in the second quadrant where sine is positive.
(b) sin2x is negative because sinx is positive and cosx is negative.
(c) sin2x is positive since sin2x=2sin2x and sinx is positive.
(d) sin2x is zero because 2x=180∘ when x is the midpoint of the interval.