cos A = -4/5 for angle A in Quadrant II, find sin 2A
in Q2 sine is negative
sin^2 + cos^2 = 1
sin^2 = 1 - 16/25 = 9/25
sin = +/- 3/5
so sin A = -3/5
sin 2A = 2 sin A cos A
=2 (-3/5)(-4/5) = 24/25
sin^2 + cos^2 = 1
sin^2 = 1 - 16/25 = 9/25
sin = +/- 3/5
so sin A = -3/5
sin 2A = 2 sin A cos A
=2 (-3/5)(-4/5) = 24/25