10-2. Parabola, Ellipse, Hyperbola
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Find the equation for the ellipse that satisfies the given conditions: $b=3,\,\, c=4,$ centre at the origin; foci on the $x$ axis.

Option A
Option B
Option C
Option D

Solution

It is given that $b=3,\,\, c=4,$ centre at the origin; foci on the $x$ axis.

since the foci are on the $x-$ axis, the major axis is along the $x-$ axis.

Therefore, the equation of the ellipse will be of the form $\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}=1,$ where a is the semimajor axis.

Accordingly, $b=3, \,\,c=4$

It is known that $a^{2}=b^{2}+c^{2}$

$\therefore a^{2}=3^{2}+4^{2}=9+16=25$

$\Rightarrow a=5$

Thus, the equation of the ellipse is $\frac{x^{2}}{5^{2}}+\frac{y^{2}}{3^{2}}=1$ or $\frac{x^{2}}{25}+\frac{y^{2}}{9}=1$

Standard 11
Mathematics

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