Hopefully you know that \(\displaystyle (a+ b)^2= a^2+ 2ab+ b^2\). For this problem you also need to know that, for any a (and, in particular, a= e), \(\displaystyle a^xa^y= a^{x+y}\).
So \(\displaystyle (e^x+ e^{-x})^2= (e^x)^2+ 2e^{x}e^{-x}+ (e^{-x})^2\).
Now, what are \(\displaystyle (e^x)^2\), \(\displaystyle e^xe^{-x}\), and \(\displaystyle (e^{-x})^2\)?
If you do not know those, then you seriously need to review algebra before continuing Calculus.
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