Posted by lauren on Wednesday, January 19, 2011 at 6:40pm.
we can see that secx > 0 and tanx < 0,
so x must be in quadrants IV
draw a right-angled triangle in that quadrant where
x = 1, y = -4, and r = √17
sinx = -4/√17
cosx = 1/√17
tanx = -4/1 = -4
you should know that:
sin(2x) = 2sinxcos = 2((-4/√17)(1/√17) = -8/17
cos(2x) = cos^2x - sin^2x = 1/17 - 16/17 = -15/17
tan(2x) = sin(2x)/cos(2x) = (-8/17)/(-15/17) = 8/15
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