1.

A curve is given by the equations  \[x=a\cos \theta +\frac{1}{2}b\cos 2\theta ,\] \[y=a\sin \theta +\frac{1}{2}b\,\sin \,2\theta \], then the points for which \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=0,\] is given by [Kurukshetra CEE 2002]

A.            \[\sin \theta =\frac{2{{a}^{2}}+{{b}^{2}}}{5ab}\]
B.            \[\tan \theta =\frac{3{{a}^{2}}+2{{b}^{2}}}{4ab}\]
C.            \[\cos \theta =\frac{-\left( {{a}^{2}}+2{{b}^{2}} \right)}{3ab}\]
D.            \[\cos \theta =\frac{\left( {{a}^{2}}-2{{b}^{2}} \right)}{3ab}\]
Answer» D.            \[\cos \theta =\frac{\left( {{a}^{2}}-2{{b}^{2}} \right)}{3ab}\]


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