How do you write the equation for a circle with center (2a, a) and touching the y-axis?

1 Answer
Nov 8, 2016

(x-2a)^2+(y-a)^2=4a^2(x2a)2+(ya)2=4a2

Explanation:

If the circle touches the Y-axis then the radius of the circle is equal to the horizontal distance from the Y-axis to the center of the circle.

The distance from the Y-axis to the center of the circle is the xx coordinate of the center of the circle.

So in this case the radius is 2a2a.

The equation for a circle with center (color(red)p,color(blue)q)(p,q) and radius color(green)rr is
color(white)("XXX")(x-color(red)p)^2+(y-color(blue)q)^2=color(green)r^2XXX(xp)2+(yq)2=r2

So the equation for a circle with cneter (color(red)(2a),color(blue)a)(2a,a) and radius color(green)(2a)2a is
color(white)("XXX")(x-color(red)(2a))^2+(y-color(blue)a)^2=color(green)(""(2a))^2XXX(x2a)2+(ya)2=(2a)2