Problem: The expression P−QP+Q​−P+QP−Q​, where P=x+y and Q=x−y, is equivalent to:
Answer Choices:
A. xyx2−y2​
B. 2xyx2−y2​
C. 1
D. xyx4+y2​
E. 2xyx2+y2​
Solution:
Since P=x+y and Q=x−y,P+Q=2x,P−Q=2y.∴P−QP+Q​−P+QP−Q​=2y2x​−2x2y​=xyx2−y2​