How do I perform a saddle point approximation to approximately find the integral $\int_{-\pi/2}^{\pi/2} \cos^n(x) dx$?

Question

I am supposed to apply the saddle point approximation (i.e. method of steepest descent) to calculate the following integral: $$\int_{-\pi/2}^{\pi/2} \cos^n(x) dx$$ But I have no idea how to write the integral in the form when the saddle point approximation can be used: $$\int_{x_1}^{x_2} e^{f(x)} dx$$