Posted by Anonymous on Thursday, January 20, 2011 at 2:55am.
cosA = -4/5 = -0.80,
A = 143.1deg.
sin(2A) = 2*sinA*cosA,
sin2A = 2*sin(143.1)*cos(143.1 =
-0.9603.
Solution using Exact values.
cosA = -4/5 = x/r.
(-4)^2 + Y^2 = 5^2,
16 + Y^2 = 25,
Y^2 = 25 - 16 = 9,
Y = 3.
SinA = Y/r = 3/5.
sin2A = 2 * 3/5 * -4/5 = -24/25.
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