Gujarati
10-2. Parabola, Ellipse, Hyperbola
medium

A tangent to a hyperbola $\frac{{{x^2}}}{{{a^2}}} - \frac{{{y^2}}}{{{b^2}}} = 1$ intercepts a length of unity from each of the co-ordinate axes, then the point $(a, b)$ lies on the rectangular hyperbola

A

${x^2} - {y^2} = 2$

B

${x^2} - {y^2} = 1$

C

${x^2} - {y^2} = - 1$

D

None of these

Solution

(b) Tangent at $(a\sec \theta ,b\tan \theta )$ is,

$\frac{x}{{(a/\sec \theta )}} – \frac{y}{{(b/\tan \theta )}} = 1$

or $\frac{a}{{\sec \theta }} = 1,\,\,\frac{b}{{\tan \theta }} = 1$

==> $a = \sec \theta $, $b = \tan \theta $

or $(a,b)$ lies on ${x^2} – {y^2} = 1$.

Standard 11
Mathematics

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