JEE Main & Advanced Mathematics Applications of Derivatives Question Bank Tangent and Normal

  • question_answer
    The equation of the tangent to the curve \[x=2{{\cos }^{3}}\theta \] and \[y=3{{\sin }^{3}}\theta \] at the point \[\theta =\pi /4\] is                                         [J & K 2005]

    A)            \[2x+3y=3\sqrt{2}\]

    B)            \[2x-3y=3\sqrt{2}\]

    C)            \[3x+2y=3\sqrt{2}\]

    D)            \[3x-2y=3\sqrt{2}\]

    Correct Answer: C

    Solution :

               \[{{\left. x\, \right|}_{\theta =\frac{\pi }{4}}}=\frac{2}{2\sqrt{2}}=\frac{1}{\sqrt{2}},\]                    \[{{\left. y\, \right|}_{\theta =\frac{\pi }{4}}}=\frac{3}{2\sqrt{2}},{{\left. \frac{dy}{dx} \right|}_{\theta =\frac{\pi }{4}}}{{\left. \frac{9\,{{\sin }^{2}}\theta \cos \theta }{-6\,{{\cos }^{2}}\theta \sin \theta } \right|}_{\theta =\frac{\pi }{4}}}=\frac{-3}{2}\].                    \[\therefore \] Equation of tangent is \[\left( y-\frac{3}{2\sqrt{2}} \right)=\frac{-3}{2}\,\left( x-\frac{1}{\sqrt{2}} \right)\]                    Þ \[3\sqrt{2}x+2\sqrt{2}y=6\]Þ \[3x+2y=3\sqrt{2}\].


You need to login to perform this action.
You will be redirected in 3 sec spinner