Q110 / 200 · Manipal (MET) 2010 · Mathematics

The locus of the point of intersection of tangents to the circle $x=a \cos \theta, y=a \sin \theta$ at the points, whose parametric angles differe by $\frac{\pi}{2}$, is

  • A
    a straight line
  • Correct answer
    B
    a circle
  • C
    a pair of straight line
  • D
    None of the above

Solution

We have, the given circle $x=a \cos \theta, y=a \sin \theta$ $\Rightarrow x^2+y^2=a^2...(i)$ Tangents to the circle (i) at $\theta$ and $\left(\theta+\frac{\pi}{2}\right)$ are $\begin{aligned} & x \cos \theta+y \sin \theta=a \\ & \text { and } x \cos \left(\theta+\frac{\pi}{2}\right)+y \sin \left(\theta+\frac{\pi}{2}\right)=a\end{aligned}$ or $x \cos \theta+y \sin \theta=a$ and $-x \sin \theta+y \cos \theta=a$ Squaring and adding, we get $x^2+y^2=2 a^2$ which is a circle.

Hence, the correct answer is option: 'B'.

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