So the question asks first to find y' of sin(x)cos(2x) which I worked out to be

cos(x)cos(2x) - 2sin(x)sin(2x)

Then question asks for y'' for which the answer is supposed to be

-5sin(x)cos(2x) - 4cos(x)sin(2x)

I am having trouble getting to that point, my answer somehow ends up a lot longer than that. Would anybody be able to help me with this problem?

Thanks!

cos(x)cos(2x) - 2sin(x)sin(2x)

Then question asks for y'' for which the answer is supposed to be

-5sin(x)cos(2x) - 4cos(x)sin(2x)

I am having trouble getting to that point, my answer somehow ends up a lot longer than that. Would anybody be able to help me with this problem?

Thanks!

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