How do you find the radius of a circle if you know the length of a chord and the shortest distance from the center of the chord to the circle?

Answer 1

Imagine if you will a circle with a chord drawn through it and a line running from the center of that chord to the center of the circle. That line is necessarily perpendicular to the chord. This means you have a right triangle whose hypotenuse is the radius of the circle. The radius is thus given by: r = sqrt{(1/2 chord length)^2 + (length of perpendicular line)^2} The actual formula to find the radius is as follows: r= C squared/8a + a/2, where C is the chord length, and a is the distance from center point of the chord to the circle , and a and C form an angle of 90 degrees. the entire formula before simplification is r = sqrt {(1/2 C)^2 + (r-a)^2}