Find $\displaystyle \frac{d^2y}{dx^2}$, as a function of $t$, for the given the parametric equations: $$\begin{array}{r@{\,}c@{\,}l} x & = & 2 - 6 \cos(t) \cr y & = & 2 + \cos^{5}(t) \end{array}$$ $\displaystyle \frac{d^2y}{dx^2} =$ .