Gujarati
10-2. Parabola, Ellipse, Hyperbola
easy

What is the slope of the tangent line drawn to the hyperbola $xy = a\,(a \ne 0)$ at the point $(a, 1)$

A

$1/a$

B

$-1/a$

C

$a$

D

$-a$

Solution

(b) Given equation of hyperbola $xy = a$

Slope of tangent at point $({x_1}\,{y_1})$ is

$m = {\left( {\frac{{dy}}{{dx}}} \right)_{({x_1},\,{y_1})}}$

$\therefore \,\frac{{xdy}}{{dx}} + y = 0$

==> $\frac{{dy}}{{dx}} = \frac{{ – y}}{x}$

At point $(a,\,1);$ $m = {\left( {\frac{{dy}}{{dx}}} \right)_{(a,\,1)}} = – \frac{1}{a}$.

Standard 11
Mathematics

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