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10-2. Parabola, Ellipse, Hyperbola
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The equation of the normal to the hyperbola $\frac{{{x^2}}}{{16}} - \frac{{{y^2}}}{9} = 1$ at $( - 4,\;0)$ is
A
$y = 0$
B
$y = x$
C
$x = 0$
D
$x = - y$
Solution
(a) $\frac{{{x^2}}}{{16}} – \frac{{{y^2}}}{9} = 1$
$ \Rightarrow $$\frac{{2x}}{{16}} – \frac{{2y}}{9}\frac{{dy}}{{dx}} = 0$
==> $\frac{{dy}}{{dx}} = \frac{{2x \times 9}}{{16 \times 2y}}$
$ = \frac{9}{{16}}\frac{x}{y}$
==> ${\left( {\frac{{ – dx}}{{dy}}} \right)_{( – 4,0)}}$
$= \frac{{ – 16}}{9}\frac{y}{x} = 0$
Hence, equation of normal
==> $(y – 0)\, = 0(x + 4)$
==> $y = 0.$
Standard 11
Mathematics
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