Sign in
Please select an account to continue using cracku.in
↓ →
Join Our JEE Preparation Group
Prep with like-minded aspirants; Get access to free daily tests and study material.
If the line $$x - 1 = 0$$ is a directrix of the hyperbola $$kx^2 - y^2 = 6$$, then the hyperbola passes through the point
We need to find which point the hyperbola passes through, given that $$x = 1$$ is a directrix of $$kx^2 - y^2 = 6$$.
$$kx^2 - y^2 = 6 \implies \frac{x^2}{6/k} - \frac{y^2}{6} = 1$$
This is of the form $$\frac{x^2}{a^2} - \frac{y^2}{b^2} = 1$$ with $$a^2 = \frac{6}{k}$$ and $$b^2 = 6$$.
$$b^2 = a^2(e^2 - 1)$$
$$6 = \frac{6}{k}(e^2 - 1)$$
$$k = e^2 - 1$$
$$e^2 = k + 1$$
For a hyperbola $$\frac{x^2}{a^2} - \frac{y^2}{b^2} = 1$$, the directrices are at $$x = \pm \frac{a}{e}$$.
Given that $$x = 1$$ is a directrix:
$$\frac{a}{e} = 1 \implies a = e$$
$$a^2 = e^2$$
$$\frac{6}{k} = k + 1$$
$$6 = k(k + 1) = k^2 + k$$
$$k^2 + k - 6 = 0$$
$$(k + 3)(k - 2) = 0$$
$$k = 2$$ (taking the positive value since $$k > 0$$ for a valid hyperbola)
$$2x^2 - y^2 = 6$$
Option A: $$(-2\sqrt{5}, 6)$$: $$2(20) - 36 = 40 - 36 = 4 \neq 6$$
Option B: $$(-\sqrt{5}, 3)$$: $$2(5) - 9 = 10 - 9 = 1 \neq 6$$
Option C: $$(\sqrt{5}, -2)$$: $$2(5) - 4 = 10 - 4 = 6 = 6$$ $$\checkmark$$
Option D: $$(2\sqrt{5}, 3\sqrt{6})$$: $$2(20) - 54 = 40 - 54 = -14 \neq 6$$
Therefore, the correct answer is Option C: $$(\sqrt{5}, -2)$$.
Create a FREE account and get:
Predict your JEE Main percentile, rank & performance in seconds
Educational materials for JEE preparation
Ask our AI anything
AI can make mistakes. Please verify important information.
AI can make mistakes. Please verify important information.