12th Class Mathematics Sample Paper Mathematics Olympiad - Sample Paper-7

  • question_answer
    The tangent to the curve \[\mathbf{5}{{\mathbf{x}}^{\mathbf{2}}}+{{\mathbf{y}}^{\mathbf{2}}}=\mathbf{1}\]at \[\left( \frac{1}{3}.\frac{-2}{3} \right)\]passes through the point

    A)  \[\left( 0,0 \right)\]                     

    B)  \[\left( 1,1 \right)\]          

    C)  \[\left( 1,-1 \right)\]                    

    D)  \[\left( -1,1 \right)\]

    Correct Answer: B

    Solution :

    [b] Given curve is \[5{{x}^{2}}+{{y}^{2}}=1\]              ......(i) To find the tangent, differentiate equation (i) \[5.2x+2y.\frac{dy}{dx}=0\] \[\Rightarrow \frac{dy}{dx}=\frac{-5x}{y}\Rightarrow {{\left( \frac{dy}{dx} \right)}_{at\left( \frac{1}{3},\frac{-2}{3} \right)}}=\frac{-5/3}{-2/3}=\frac{5}{2}\] So, equation of the tangent will be \[y-{{y}_{1}}=m(x-{{x}_{1}})\] \[\Rightarrow y+\frac{2}{3}=\frac{5}{2}\left( x-\frac{2}{3} \right)\Rightarrow 2(3y+2)=5(3x-1)\] \[\Rightarrow 15x-6y-5-4=0\text{ }\Rightarrow 15x-6y-9=0\] Since, point (1,1) satisfies the equation of the tangent of the given curve. Hence, option [b] is correct.


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