Thread: Evaluate

Given f(x) = cos x and g(x) = π/2, evaluate f(g(3)).

You don't even have to compose functions. Note that $\displaystyle g(\alpha)=\frac\pi2$ for every $\displaystyle \alpha\in\mathbb R,$ so $\displaystyle g(3)=\frac\pi2.$ Hence $\displaystyle f\big(g(3)\big)=f\left(\frac\pi2\right)=0.$