Question

Find the radius of the circle with equation x^2+y^2-4x-10y+4=0.

(a) 25 units

(b) 20 units

(c) 5 units

(d) 10 units

This question was addressed to me by my school teacher while I was bunking the class.

This interesting question is from Conic Sections topic in division Conic Sections of Mathematics – Class 11

Answer 1

Correct answer is (c) 5 units

To explain: Comparing the equation with general form x^2+y^2+2gx+2fy+c=0, we get

2g=-4 => g=-2

2f=-10 => f=-5

c=4

Radius = \(\sqrt{g^2+f^2-c} = \sqrt{4+25-4}\)=5.