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10-2. Parabola, Ellipse, Hyperbola
normal
Consider an ellipse with foci at $(5,15)$ and $(21,15)$. If the $X$-axis is a tangent to the ellipse, then the length of its major axis equals
A
$17$
B
$34$
C
$13$
D
$\sqrt{416}$
(KVPY-2009)
Solution

(b)
Given, $(5,15)$ and $(21,15)$
are foci of parabola and $X$-axis is tangent of ellipse.
$2 a e =16 \text { and } b=15$
$a e =8 \text { and } b=15$
$a e^2 =a^2-b^2$
$16 =a^2-225$
$a^2 =289$
$a =17$
$\therefore$ Length of major axis $=34$
Standard 11
Mathematics