GRE Question of the Day (July 24th)

If \({x + 2y = a}\) and \({x – 2y = b}\), which of the following expressions is equal to \({xy}\)?

A. \({ab}\)

B. \({\frac{{a+b}}{{2}}}\)

C. \({\frac{{a-b}}{{2}}}\)

D. \({\frac{{a^2-b^2}}{{4}}}\)

E. \({\frac{{a^2-b^2}}{{8}}}\)