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Geometry Science Fair Project

Polygon Sides and Pi Estimation Error

Hard
Polygon Sides and Pi Estimation Error | Science Fair Projects | STEM Projects
How fast does your estimate of pi improve when you use polygons with more sides? Ancient math used shapes drawn inside and around circles to estimate pi. The more sides the polygon has, the closer the estimate gets. You calculate pi by averaging the perimeters of polygons inscribed in and drawn around a circle. Then you compare the errors from polygons with different numbers of sides. You test six different pairs and track how the error ratio changes as the side count grows. The error ratio follows a clear pattern. It approaches the square of the inverse of the side-count ratio. This means the error shrinks in a predictable way as you add more sides.

Hypothesis

The hypothesis is that the ratio between the error in determining pi using by inscribing polygons within and circumscribing polygons about a circle with (km) sides and that obtained using polygons with (kn) sides will approach (n/m)^2 as k increases.

Method & Materials

You will develop formulas to determine the perimeters of the regular polygons inscribed within and circumscribed about a circle. You will estimate pi by using the expression: (X(sin(180/X) + X(tan(180/X))) / 2, and calculate the error in estimating pi using polygons with the formula: error = ((X(sin(180/X) + X(tan(180/X))) / 2) - pi.
You will need formulas to determine the perimeters of the regular polygons inscribed within and circumscribed about a circle, and a calculator.

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Results

The results of the experiment showed that the graphs were consistent with the hypothesis. As the number of sides increased, the error ratio approached the square of the inverse of the ratio of the number of sides.

Why do this project?

This science project is interesting because it explores the ratio between the error in estimating pi using polygons with different numbers of sides.

Also Consider

Experiment variations to consider include changing the number of sides of the polygons, or changing the diameter of the circle.

Full project details

Additional information and source material for this project are available below.
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