Gujarati
10-2. Parabola, Ellipse, Hyperbola
medium

The equation of the hyperbola whose directrix is $x + 2y = 1$, focus $(2, 1)$ and eccentricity $2$ will be

A

${x^2} - 16xy - 11{y^2} - 12x + 6y + 21 = 0$

B

$3{x^2} + 16xy + 15{y^2} - 4x - 14y - 1 = 0$

C

${x^2} + 16xy + 11{y^2} - 12x - 6y + 21 = 0$

D

None of these

Solution

(a) ${(x – 2)^2} + {(y – 1)^2} = 4\left[ {\frac{{{{(x + 2y – 1)}^2}}}{5}} \right]$

==> $5[{x^2} + {y^2} – 4x – 2y + 5]$

$ = 4[{x^2} + 4{y^2} + 1 + 4xy – 2x – 4y]$

==> ${x^2} – 11{y^2} – 16xy – 12x + 6y + 21 = 0$.

Standard 11
Mathematics

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