The correct Option is : 4
While alkaloids, terpenoids, and glycosides can have inhibitory effects, they aren't primarily classified as natural plant growth inhibitors. However, given the options:
Given, the function \( f(x) = \frac{a^x + a^{-x}}{2} \) (\( a > 2 \)), then \( f(x+y) + f(x-y) \) is equal to