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Cos I can

Calculus Level 4

If

$\sum_{n=1}^{\infty} \frac{\cos n}{n}$

can be expressed in the form $-\frac 12 \ln(a-b\cos c)$ , where $a,b,$ and $c$ are positive integers, find $a+b+c$ .

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Excel in math and science

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by Jake Lai

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