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← JEE Main 2015 · 10 Apr · Shift 1
MathematicsSingle correct+4 / -1Question 71 of 90

JEE Main 2015 · 10 Apr · Shift 1, Mathematics question 71

The distance, from the origin, of the normal to the curve, x=2cos⁡t+2tsin⁡tx=2\cos t+2t\sin t, y=2sin⁡t−2tcos⁡ty=2\sin t-2t\cos t at t=π4t=\dfrac\pi4, is :

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Answer and worked solution

Official answer: C

dxdt=2tcos⁡t\dfrac{dx}{dt}=2t\cos t and dydt=2tsin⁡t\dfrac{dy}{dt}=2t\sin t, so the tangent slope is tan⁡t\tan t and the normal is xcos⁡t+ysin⁡t=px\cos t+y\sin t=p. At the point,
xcos⁡t+ysin⁡t=2cos⁡2t+2tsin⁡tcos⁡t+2sin⁡2t−2tsin⁡tcos⁡t=2.x\cos t+y\sin t=2\cos^2t+2t\sin t\cos t+2\sin^2t-2t\sin t\cos t=2.
The distance is 2.