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10-2. Parabola, Ellipse, Hyperbola
easy
The locus of the point of intersection of any two perpendicular tangents to the hyperbola is a circle which is called the director circle of the hyperbola, then the eqn of this circle is
A
${x^2} + {y^2} = {a^2} + {b^2}$
B
${x^2} + {y^2} = {a^2} - {b^2}$
C
${x^2} + {y^2} = 2ab$
D
None of these
Solution
(b) Equation of hyperbola is $\frac{{{x^2}}}{{{a^2}}} – \frac{{{y^2}}}{{{b^2}}} = 1$
Any tangent to hyperbola are $y = mx \pm \sqrt {{a^2}{m^2} – {b^2}} $
Also tangent perpendicular to this is $y = \frac{{ – 1}}{m}x \pm \sqrt {\frac{{{a^2}}}{{{m^2}}} – {b^2}} $
Eliminating $m$, we get ${x^2} + {y^2} = {a^2} – {b^2}$.
Standard 11
Mathematics