- Home
- Standard 11
- Mathematics
10-2. Parabola, Ellipse, Hyperbola
normal
Latus rectum of the conic satisfying the differential equation, $ x dy + y dx = 0$ and passing through the point $ (2, 8) $ is :
A
$4 \sqrt 2 $
B
$8$
C
$8 \sqrt 2 $
D
$16$
Solution

$\frac{{dy}}{y}\,\, + \,\frac{{dx}}{x}\, = \,0 $ $\Rightarrow$ $ ln$ $ xy = c$ $\Rightarrow$ $ xy = c$
passes through $(2,8)$ $ \Rightarrow$ $ c = 16$
$xy =16$ $LR = 2a(e^2 – 1) = 2a$
solving with $y = x$
vertex is $(4, 4)$
distance from centre to vertex = $4\sqrt 2 \,$
$L.R. = $ length of $TA =8\sqrt 2 \,$
Standard 11
Mathematics