Q. The coordinates of the focus of the parabola described parametrically by $x = 5t^{2} + 2,\ y + \ 10t\ + \ 4$ are

A) (7,4)
B) (3,4)
C) $(3, - 4)$
D) $( - 7,4)$
Explanation

(a)
Given parametric curves are
$x = 5t^{2} + \ 2,\ \ y = 10\ t + 4$
or $\frac{x - 2}{5} = t^{2},\ \frac{y - 4}{10} = t$
$\Rightarrow \ \frac{x - 2}{5} = \ \left( \frac{y - 4}{10} \right)^{2}$
$\Rightarrow \ (y - 4)^{2} = 20(x - 2)$
$\Rightarrow \ Y^{2} = 20X,\ where\ Y = y - 4,\ X = x - 2$
$\therefore$ Coodinates of focus are (5, 0)
$ie$, $x - 2 = 5,\ y - 4 = 0$
$\Rightarrow \ \ x = 7,\ y = 4$
Hence, required coordinates are (7, 4)

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.

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