Find Radius of a Circle by its Center and any point on it

How to find the Radius of a Circle if its Center and any other point are given

QUESTION: What is the radius of a circle whose center is at C(-1, 3) passing through point P (7,11)?

SOLUTION:

Here center C = (a, b) = (-1 , 3)

So, 

a = -1

b = 3

Point P passing through the circle = (c, d) = (7, 11)

So, 

c = 7

d = 11

Distance between point C and P is the radius of the circle.

As we know, formula of finding distance between point (a, b) and point (c, d) =

Thus, the radius r of a circle = CP 

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