The equation of the curve in which the portion of the tangent included between the coordinate axes is bisected at the point of contact, is |
a parabola an ellipse a circle a hyperbola |
a hyperbola |
The equation of the tangent at any point $P(x, y)$ is $Y-y=\frac{d y}{d x}(X-x)$ This cuts the coordinate axes at $A\left(x-y \frac{d x}{d y}, 0\right)$ and $B\left(0, y-x \frac{d y}{d x}\right)$ It is given that $P(x, y)$ is the mid-point of $A B$. ∴ $x-y \frac{d x}{d y}=2 x$ and $y-x \frac{d y}{d x}=2 y$ $\Rightarrow x+y \frac{d x}{d y}=0$ and $y+x \frac{d y}{d x}=0$ $\Rightarrow x d y+y d x=0$ and $y d x+x d y=0$ $\Rightarrow d(x y)=0 \Rightarrow x y=C$ Clearly, it represents a rectangular hyperbola. |