Question:medium

If \( f(x) = \frac{a^x + a^{-x}}{2} \) and \( f(x+y) + f(x-y) = k f(x)f(y) \), then \( k \) is equal to

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Expressions of type $\frac{a^x+a^{-x}}{2}$ behave like $\cosh x$.

Updated On: Apr 23, 2026

$2$
$4$
$-2$
None of these

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The Correct Option is D

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