Question
Question: If the line lx + my = 1 be a tangent to the circle x<sup>2</sup> + y<sup>2</sup> = a<sup>2</sup>, th...
If the line lx + my = 1 be a tangent to the circle x2 + y2 = a2, then the locus of the point (l, m) is-
A
A straight line
B
A Circle
C
A parabola
D
An ellipse
Answer
A Circle
Explanation
Solution
If the line lx + my – 1 = 0 touches the circle
x2 + y2 = a2 then p = r
= a on square 1 = a2(l2 + m2)
Ž l2+m2 = 1/a2
Ž\ locus x2 + y2 = 1/a2 (circle)