Circles for the Clueless Geometry Student

Finding the center of a circle

The saying, "He can't see the forest for the trees" is another way of saying that someone is too bogged down in the details to see the "big picture." We find that self-appointed freelance journalists, especially the ones answering questions for the former Demand Media¹ people, often suffer from forest and tree confusion – especially when they're writing on unfamiliar topics. Today's DotD is a classic example of this syndrome: Rachel Pancare, who wrote "How to  Determine the Diameter of a Circle"² for what is now the site Sciencing.com (who thinks this topic is "physics").

Pancare, who holds both a BA in English and a MS in Education, dutifully described all the trees. She waxed eloquent on the relationship of the radius of a circle to its diameter and circumference, and even explained how to calculate the diameter of a circle of known area. We won't argue with any of her assertions, since they're demonstrably correct (although we were a little nonplussed by the claim that "radius x 2, = diameter"; given that odd comma placement).

Regardless of the accuracy of Rachel's statements and calculations, we contend that she omitted critical information from her post. Says Pancare,

"You can find the diameter of a circle by using other measurements of the circle. Before you begin calculating, be certain you understand the parts of a circle. The diameter is the distance across the circle from a point on one side to a point on the opposite side, passing through the exact middle point of the circle. You can use the radius, circumference or area to help you find this measurement." Well, yeah: but what if you don't know any of those quantities? If you depend on Pancare's post, you're basically out of luck -- the one exception being that, if you have a physical circle like a wheel, you can (probably) measure the circumference. Otherwise, you're up the creek...

...unless you know how to find the center of your circle, in which case you can actually measure the radius or diameter. Here's a little secret: it's actually pretty easy to find the center of any circle: all you need is a piece of paper, a pencil, and a straightedge. And that. readers, is the forest!

Pancare never stopped to think that people might find themselves trying to measure the diameter of a circle without already knowing its area, radius, or circumference -- in which case they must know the center of the circle to measure radius and diameter. We think that her omission is all the reason we need to give her the Dumbass of the Day award.

¹ Demand Media, the parent of eHow and other similar sites, now calls itself "Leaf Group" and has begun parceling out its content to so-called niche sites. They're still just as dumb, though...
² Leaf called in one of their "repair specialists" to clean up Pancare's post. We featured her in her own DotD award, but you can still find Rachel's version using the Wayback Machine at archive.org. Just search on the URL  ehow.com/how_5743525_determine-diameter-circle.html

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