A point on the parabola y2=18x at which the ordinate increases at twice the rate of the abscissa is:
A
(2,4)
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B
(2,−4)
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C
(−98,92)
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D
(98,92)
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Solution
The correct option is B(98,92) Equation of parabola is y2=18x Differentiating w.r.t t 2ydydt=18dxdt⇒2.2y=18⇒y=92(∵dydt=2dxdt) Therefore from equation of parabola (92)2=18x⇒814=18x⇒x=814×18⇒x=98 Therefore point is (98,92)