Use the identity cos 2x = cosx * cos x - sin x * sin x to find the derivative of cos 2x. Express the derivative in terms of sin 2x. I have no idea how to do this.
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Originally Posted by Truthbetold Use the identity cos 2x = cosx * cos x - sin x * sin x to find the derivative of cos 2x. Express the derivative in terms of sin 2x. I have no idea how to do this. just let and use the product rule
Originally Posted by Jhevon just let and use the product rule Product rule of both sides? Get: -cos sin + cos sin - (-cos sin - cos sin) And get: 0 That cannot be the right answer. What am I doing wrong?
Originally Posted by Truthbetold Product rule of both sides? Get: -cos sin + cos sin - (-cos sin - cos sin) And get: 0 That cannot be the right answer. What am I doing wrong? the derivative of sin(x) is +cos(x) and it's a bad habit to write sin and cos alone like that.
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