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What is the easiest way to find the maximum of $9\cos(t) - 8\cos (3t)$?

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What have you tried so far? – Rahul Narain Oct 28 '10 at 2:06
The standard first derivative test worked for me. You may want to look up the triple angle formulas if you get stuck. If you know some complex variables, you can derive these fairly easily with DeMoivre's formula and Euler's formula – WWright Oct 28 '10 at 2:12

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Express $\cos(3t)$ in terms of $\cos(t)$ and differentiate with respect to $t$ or $\cos(t)$.

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