My math is right. The area of a circle is pi divided by four times the diameter squared (D * D). You can calculate the area of a circle with either the radius or the diameter (after all they are always related by a constant factor of 2) - it doesn't matter as long as you divide by four when you use diameter, as I showed. You either divide the diameter by two to obtain the radius before you square the dimension or you divide by 2 squared (i.e., 4) after you square the dimension. I've calculated the area of a circle more times than probably 99% of the population, and I've found it simpler to use the (pi/4) * D^2 approach when the data lists diameter instead of radius, as it usually does for my uses.
RR, I owe you an apology. You are correct! Although I find it simpler to use the radius method. Must be the Civil in me...
