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3.14 Perimeter of a particular ellipse

Example.

Use Simpson’s rule to estimate the perimeter of the ellipse

(x5)2+(y3)2=1.\left(\frac{x}{5}\right)^{2}+\left(\frac{y}{3}\right)^{2}=1.

In this case a=5a={5} and b=3,b={3,} so that

κ=1-b2a2=1-925=1625=45.\kappa=\sqrt{1-\frac{b^{2}}{a^{2}}}=\,{\sqrt{1-\frac{9}{25}}=}\,{\sqrt{\frac{1% 6}{25}}=\frac{4}{5}.}

By Prop. 3.11, the perimeter of the ellipse is 20E(45)20E({\frac{4}{5}}). (You are not expected to remember Prop. 3.11, but you could otherwise answer this question by parametrizing the ellipse via x=5sintx=5\sin t, y=3costy=3\cos t.)

We therefore apply Simpson’s rule to estimate E(45)E(\frac{4}{5}).