Equations of the latus rectum of the ellipse $9 x^2+4 y^2-18 x-8 y-23=0$ are :
Equations of the latus rectum of the ellipse $9 x^2+4 y^2-18 x-8 y-23=0$ are :
- $y= \pm \sqrt{5}$
- $x= \pm \sqrt{5}$
- $y=1 \pm \sqrt{5}$
- $x=-1 \pm \sqrt{5}$
Solution
Equation of ellipse is
$9 x^2+4 y^2-18 x-8 y-23=0$
$\Rightarrow \quad 9\left(x^2-2 x+1\right)-9+4\left(y^2-2 y+1\right)$ $-4-23=0$
$\Rightarrow \quad 9(x-1)^2+4(y-1)^2=36$
$\Rightarrow \quad \frac{(x-1)^2}{4}+\frac{(y-1)^2}{9}=1$
Here $\quad a < b$
Also$e=\sqrt{1-\frac{4}{9}}=\sqrt{\frac{5}{9}}=\frac{\sqrt{5}}{3}$
Equation of latus rectum are
$y-1= \pm 3 \cdot \frac{\sqrt{5}}{3}$
$y=1 \pm \sqrt{5}$
Asked in: AP EAMCET 2006
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