Visualising Successive Approximations

Visualising Successive Approximations

The black curve in each panel is \(y=\cos x\). The dashed blue curve is a Maclaurin polynomial. Matching more derivatives at \(x=0\) generally extends the close agreement around the origin, although it does not guarantee better accuracy for every \(x\).

\(P_2(x)=1-\dfrac{x^2}{2!}\)

\(P_4(x)=1-\dfrac{x^2}{2!}+\dfrac{x^4}{4!}\)

\(P_6(x)=1-\dfrac{x^2}{2!}+\dfrac{x^4}{4!}-\dfrac{x^6}{6!}\)

\(P_8(x)=1-\dfrac{x^2}{2!}+\dfrac{x^4}{4!}-\dfrac{x^6}{6!}+\dfrac{x^8}{8!}\)

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Answer:\(P_2(x)=1-\frac{x^2}{2}\), \(P_4(x)=1-\frac{x^2}{2}+\frac{x^4}{24}\), and \(P_6(x)=1-\frac{x^2}{2}+\frac{x^4}{24}-\frac{x^6}{720}\). Each added term makes the Maclaurin polynomial approximate \(\cos x\) over a wider interval around \(x=0\).

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