Find Radius of Circle for Given Equation
Prequisite Knowledge
Equation of a Circle
Problem
Find the radius of a circle with the following equation:
x
2
− 4
x
+
y
2
− 8
y
− 10 = 0
Solution
You need to rewrite the given equation so that it is of the form of
Eq2 in the lesson Equation of a Circle
.
(
x
2
− 4
x
+ 4) + (
y
2
− 8
y
+ 16) − 10 = 4 + 16
(
x
− 2)
2
+ (
y
− 4)
2
= 30
Once you do that you know that 30 equals the square root of the radius.
r
= √
30
= 5.477
r
= 5.477