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My problem is to find the relative extrema of abs(sin 2x); 0< x < 2pi.

I got the derivative right, I think: 2 cos 2x if x > 0, and -2 cos 2x if x < 0.

However, the solution says that f ' (x) does not exist at x = pi/2, x = pi, and x = (3pi)/2.

Glancing at my trigonometry charts, I see that sin and cos are never undefined,

so why does 2 cos 2x or -2 cos 2x not exist at pi/2, pi, or 3pi/2?

Thanks,

Nick

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# Relative extrema confusion

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