Chapter 11 - Infinite Sequences and Series - 11.1 Exercises - Page 724: 6

{0, -1, 0, 1, 0}

Plug in $n$ = 1: $a_{1}=cos\frac{(1)\pi}{2} =0$ Plug in $n$ = 2: $a_{1}=cos\frac{(2)\pi}{2} =-1$ Doing the same for $n = 3,4,5:$ $a_{3}=cos\frac{(3)\pi}{2} =0$ $a_{4}=cos\frac{(4)\pi}{2} =1$ $a_{5}=cos\frac{(5)\pi}{2} =0$ Therefore, the first 5 terms of the sequence are: {0, -1, 0, 1, 0}