If \(a>0, b>0\) then the maximum area of the parallelogram whose three vertices are \(O(0,0) . A(a \cos \theta, b \sin \theta)\) and \(\mathrm{B}(\mathrm{a} \cos \theta,-\mathrm{b} \sin \theta)\) is
(A) \(a b\) when \(\theta=\pi / 4\)
(B) \(3 a b\) when \(\theta=\pi / 4\)
(C) \(a b\) when \(\theta=\pi / 2\)
(D) \(2 a b\)
Ans: (A)
