The point on the curve $y^2 = 8x$ for which the abscissa and ordinate change at the same rate, is |
(2, -4) (2, 4) $(1,2\sqrt{2})$ $(1,-2\sqrt{2})$ |
(2, 4) |
The correct answer is Option (2) → (2, 4) $y^2 = 8x$ $\frac{dy}{dx}$ is required. $2y\frac{dy}{dx} = 8$ $\frac{dy}{dx} = \frac{4}{y}$ Equal rate of change of abscissa and ordinate means: $\frac{dy}{dx} = \pm 1$ Case 1: $\frac{4}{y}=1 \Rightarrow y=4$ $x=\frac{y^2}{8}=\frac{16}{8}=2$ Case 2: $\frac{4}{y}=-1 \Rightarrow y=-4$ $x=\frac{16}{8}=2$ The points where abscissa and ordinate change at the same rate are $(2,4)$ and $(2,-4)$. |