Question:
Find the equation for the ellipse that satisfies the given conditions: Foci (±3, 0), a = 4
Solution:
Foci (±3, 0), a = 4
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 semi-major axis.
Accordingly, c = 3 and a = 4.
It is known that $a^{2}=b^{2}+c^{2}$.
$\therefore 4^{2}=b^{2}+3^{2}$
$\Rightarrow 16=b^{2}+9$
$\Rightarrow b^{2}=16-9=7$
Thus, the equation of the ellipse is $\frac{x^{2}}{16}+\frac{y^{2}}{7}=1$.
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