## Calculus: Early Transcendentals 8th Edition

The first five terms are $0, -1, 0, 1, 0.$
To find the first five terms of $a_n = \cos{(\frac{n\pi}{2})}$, we must plug in $n=1, n=2, n=3, n=4$ and $n=5.$ Hence the first five terms are $\cos{(\frac{\pi}{2})}, \cos{(\pi)}, \cos{(\frac{3\pi}{2})}, \cos{(2\pi)}$, and $\cos{(\frac{5\pi}{2})}$, i.e. $$0, -1, 0, 1, 0.$$