MCQ
Radius parametric equation represented by $x=2 a\left(\frac{1-t^2}{1+t^2}\right), y=\frac{4 a t}{1+t^2}$ is
  • A
    $a$
  • B
    $a ^2$
  • C
    3a
  • 2a

Answer

Correct option: D.
2a
(D)
$x=2 a\left(\frac{1-t^2}{1+t^2}\right)$ ...(i)
$y=\frac{4 at }{1+ t ^2}$ ...(ii)
Squaring and adding (i) and (ii), we get
$x^2+y^2=4 a ^2 \cdot \frac{\left(1- t ^2\right)^2}{\left(1+ t ^2\right)^2}+\frac{16 a ^2 t ^2}{\left(1+ t ^2\right)^2}$
$=\frac{4 a^2}{\left(1+t^2\right)^2}\left[1-2 t^2+t^4+4 t^2\right]$
$=\frac{4 a^2}{\left(1+t^2\right)^2}\left(1+t^2\right)^2$
$\therefore \quad x^2+y^2=(2 a)^2$
$\therefore \quad$ Radius $=2 a$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free