# Write the Eccentricity of the Ellipse 9x2 + 5y2 − 18x − 2y − 16 = 0. - Mathematics

Write the eccentricity of the ellipse 9x2 + 5y2 − 18x − 2y − 16 = 0.

#### Solution

$9 x^2 + 5 y^2 - 18x - 2y - 16 = 0$
$\Rightarrow 9\left( x^2 - 2x \right) + 5\left( y^2 - \frac{2y}{5} \right) = 16$
$\Rightarrow 9\left( x^2 - 2x + 1 \right) + 5\left( y^2 - \frac{2y}{5} + \frac{1}{25} \right) = 16 + 9 + \frac{1}{5}$
$\Rightarrow 9 \left( x - 1 \right)^2 + 5 \left( y - \frac{1}{5} \right)^2 = \frac{126}{5}$
$\Rightarrow \frac{\left( x - 1 \right)^2}{\frac{126}{45}} + \frac{\left( y - \frac{1}{5} \right)^2}{\frac{126}{25}} = 1$
$\Rightarrow a^2 = \frac{126}{45} \text{ and } b^2 = \frac{126}{25}$
$\text{ Clearly }, a < b$
$\text{ Now }, e = \sqrt{1 - \frac{a^2}{b^2}}$
$\Rightarrow e = \sqrt{1 - \frac{\frac{126}{45}}{\frac{126}{25}}}$
$\Rightarrow e = \sqrt{1 - \frac{5}{9}}$
$\Rightarrow e = \frac{2}{3}$

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#### APPEARS IN

RD Sharma Class 11 Mathematics Textbook
Chapter 26 Ellipse
Q 2 | Page 27