Equation to determine radius for a circle that should intersect a given point? Simple question. I tried Google but I don't know what search keywords to use.
I have two points on a $2D$ plane. Point 1 $=(x_1, y_1)$ and Point 2 $=(x_2, y_2)$.

I'd like to draw a circle around Point 1, and the radius of the circle should be so that it intersects exactly with Point 2.

What is the equation to determine the required radius?

If $P_1(x_1,y_1)$ is the center, the radius will be $\sqrt{(x_2-x_1)^2+(y_2-y_1)^2}$
