Q85 / 200 · WBJEE 2014 · Mathematics

The point on the parabola $y^{2}=64 x$ which is nearest to the line $4 x+3 y+35=0$ has coordinates

  • Correct answer
    A
    (9,-24)
  • B
    (1,81)
  • C
    (4,-16)
  • D
    (-9,-24)

Solution

Given equation of parabola is $$ y^{2}=64 x $$ The point at which the tangent to the curve is parallel to the line is the nearest point on the curve. On differentiating both sides of Eq. (i), we get $2 y \frac{d y}{d x}=64$ $\Rightarrow \quad \frac{d y}{d x}=\frac{32}{y}$ Also, slope of the given line is $-\frac{4}{3}$. $\therefore$ $$ -\frac{4}{3}=\frac{32}{y} \Rightarrow y=-24 $$ From Eq. (i), $(-24)^{2}=64 x \Rightarrow x=9$ $\therefore$ Hence, the required point is (9,-24)

Hence, the correct answer is option: 'A'.

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