question_answer

Given the function \[f(x)=\frac{{{a}^{x}}+{{a}^{-x}}}{2},\ (a>2)\]. Then \[f(x+y)+f(x-y)=\]

A)            \[2f(x).f(y)\]

B)            \[f(x).f(y)\]

C)            \[\frac{f(x)}{f(y)}\]

D)            None of these