Question 3
A sequence begins with $a_{1}$=$a_{2}$=1. Its later terms satisfy $a_{n+2}$=$a_{n}$+$(−1)^{n}$ $a_{n+1}$. For example, $a_{3}$=$a_{1}$−$a_{2}$, $a_{4}$=$a_{2}$+$a_{3}$, $a_{5}$=$a_{3}$−$a_{4}$, and so on. What is the sum of its first 100 terms?
