A point on the parabola $y^2=18 x$ at which the ordinate increases at twice the rate of the abscissa is
A point on the parabola $y^2=18 x$ at which the ordinate increases at twice the rate of the abscissa is
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$(2,4)$
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$(2,-4)$
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$\left(\frac{-9}{8}, \frac{9}{2}\right)$
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$\left(\frac{9}{8}, \frac{9}{2}\right)$
Solution
Any point be $\left(\frac{9}{2} t^2, 9 t\right) ;$ differentiating $y^2=18 x$
$
\begin{aligned}
& \Rightarrow \frac{\mathrm{dy}}{\mathrm{dx}}=\frac{9}{\mathrm{y}}=\frac{1}{\mathrm{t}}=2 \text { (given) } \Rightarrow \mathrm{t}=\frac{1}{2} . \\
& \Rightarrow \text { Point is }\left(\frac{9}{8}, \frac{9}{2}\right)
\end{aligned}
$
Asked in: JEE Main 2004
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