1.

If a circle pass through (4, 0) and (0, 2) and center at y-axis then find the radius of the circle.(a) 25 units(b) 20 units(c) 5 units(d) 10 unitsI have been asked this question in a national level competition.I'd like to ask this question from Conic Sections in chapter Conic Sections of Mathematics – Class 11

Answer»

The CORRECT answer is (c) 5 UNITS

The best explanation: Equation of circle with center at y-axis (0, B) and radius r units is

(x)^2+(y-b)^2=r^2

=>(4)^2+(-b)^2=r^2

And (0)^2+(2-b)^2=r^2

=>(b-2)^2=b^2+4^2 => (-2)(2b-2)=16 => b-1=-4 => b=-3

So, r^2=4^2+3^2=5^2 => r=5 units.


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