If \(x + 2y = a\) and \(x - 2y = b\), which of the following is an expression for \(xy\)?
(A)\(ab\) (B)\(\frac { a + b } { 2 } \) (C)\(\frac { a - b } { 2 } \) (D)\(\frac { a^2 - b^2 } { 4 } \) (E)\(\frac { a^2 - b^2 } { 8 } \)
E