Problem: Given the system of equations ax+(a−1)y=1(a+1)x−ay=1. For which one of the following values of a is there no solution for x and y?
Answer Choices:
A. 1
B. 0
C. −1
D. 2±2
E. ±2
Solution:
There is no solution when a(−a)−(a−1)(a+1)=0, that is, when a=±2/2
or
solve for x, obtaining x=(2a−1)/(2a2−1), which is undefined when 2a2−1=0, that is, when a=±2/2.