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Q.The slope of the tangent to the curve x=t2+3t−8x = t^2 + 3t - 8, y=2t2−2t−5y = 2t^2 - 2t - 5 at the point (2,−1)(2, -1) is

(a) 227\frac{22}{7}
(b) 67\frac{6}{7}
(c) −76-\frac{7}{6}
(d) 76\frac{7}{6}
Manipur CohsemCOHSEM Manipur Higher Secondary Board 2022MCQ· 1mImportance★★★★★
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Use dydx=dy/dtdx/dt\dfrac{dy}{dx}=\dfrac{dy/dt}{dx/dt} for the parametric curve, first finding the parameter tt at the given point.

Given x=t2+3t−8x=t^2+3t-8, y=2t2−2t−5y=2t^2-2t-5.

dxdt=2t+3,dydt=4t−2\frac{dx}{dt}=2t+3,\qquad \frac{dy}{dt}=4t-2

Find tt at the point (2,−1)(2,-1).

From x=2x=2: t2+3t−8=2⇒t2+3t−10=0⇒(t+5)(t−2)=0⇒t=2,−5t^2+3t-8=2\Rightarrow t^2+3t-10=0\Rightarrow (t+5)(t-2)=0\Rightarrow t=2,-5.

From y=−1y=-1: 2t2−2t−5=−1⇒2t2−2t−4=0⇒t2−t−2=0⇒(t−2)(t+1)=0⇒t=2,−12t^2-2t-5=-1\Rightarrow 2t^2-2t-4=0\Rightarrow t^2-t-2=0\Rightarrow (t-2)(t+1)=0\Rightarrow t=2,-1.

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