<s>[INST] How to solve this equation $2\cos(\frac {x^2+x}{6})=2^x+2^{-x}$ How do I solve for $x$ from this equation?
$$2\cos\frac {x^2+x}{6}=2^x+2^{-x}$$
 [/INST] $-2\le2\cos(\frac{x^2 + x}{6})\le 2$ and $2\le2^x + 2^{-x}$.
Therefore the only possible solution is when both equal $2$.
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