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Question: Locus of centre of variable circle tx<sup>2</sup> + ty<sup>2</sup> + 2(t<sup>2</sup> + 1)x – 2(t<sup...

Locus of centre of variable circle tx2 + ty2 + 2(t2 + 1)x – 2(t2 –1)y – 5t = 0 is a :

A

Straight line

B

Circle

C

Parabola

D

Hyperbola

Answer

Hyperbola

Explanation

Solution

Circle x2 + y2 +2(t2+1)t\frac{(t^{2} + 1)}{t}x – 2 (t21)t\frac{(t^{2}–1)}{t}y – 5 = 0

centre (t1t,t1t)\left( –t–\frac{1}{t},t–\frac{1}{t} \right)

locus x2 – y2 = (t+1t)2\left( t + \frac{1}{t} \right)^{2}(t1t)2\left( t–\frac{1}{t} \right)^{2} = 4

Ž Hyperbola