Posted by **Anonymous** on Saturday, November 24, 2007 at 7:07pm.

What am I doing wrong?

Equation:

sin2x = 2cos2x

Answers:

90 and 270

....

My Work:

2sin(x)cos(x) = 2cos(2x)

sin(x) cos(x) = cos(2x)

sin(x) cos(x) = 2cos^2(x) - 1

cos(x) (+/-)\sqrt{1 - cos^2(x)} = 2cos^2(x) - 1

cos^2(x)(1 - cos^2(x)) = 4cos^4(x) - 4cos^2(x) + 1

5cos^4(x) - 5cos^2(x) + 1 = 0

cos(x) = (+/-) 0.85065080835215

cos(x) = (+/-)0.52573111211905

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