Problem: In the expression x−1x+1​ each x is replaced by x−1x+1​. The resulting expression, evaluated for x=21​, equals:
Answer Choices:
A. 3
B. −3
C. 1
D. −1
E. none of these
Solution:
x−1x+1​−1x−1x+1​+1​=x+1−(x−1)x+1+(x−1)​=x