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**1. Homework Statement**

Prove the following using induction:

[tex]cos(n\pi + x) = (-1)^ncos(x) [/tex]

**3. The Attempt at a Solution**

Let [tex] cos(k\pi + x) = (-1)^k cos(x)[/tex]

True for k=1

Right Hand Side...

[tex](-1)^{k+1}cos(x)[/tex]

[tex]= -(-1)^k cos(x)[/tex]

[tex]= (-1)^k cos(x)[/tex]

Since [tex](-1)^{k+1}cos(x) = (-1)^k cos(x)[/tex]...

Not too sure where to go from here.

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