Diameter of a circle using 3 nonlinear points I am trying to find the diameter of a circle using 3 points on its circumference.  2 of the points are 5 feet from eachother while the third point is centered between the other 2.  The ceter point is 1 foot from a line drawn between the other 2 points.

Hint: If two chords $AB$ and $CD$ of a circle intersect at $P$, then $AP\cdot PB=CP\cdot PD$.  Draw the diameter joining the red and green lines in your diagram. So, $AP=PB=\dfrac{5}{2}$ and $CP=1$, and hence $DP=\dfrac{25}{4}$. Now you can compute the diameter. 

