Chapter 8: Infinite Sequences and Series
Section 8.5: Taylor Series
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Example 8.5.17
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a)
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Obtain and , degree 8 Maclaurin polynomials for and , respectively.
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b)
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Form the product .
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c)
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Obtain the degree 11 Maclaurin polynomial for the product .
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d)
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Obtain the first 10 coefficients formed from the Cauchy product of the coefficients of and .
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e)
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Observe that the coefficients formed from the Cauchy product (Theorem 8.2.4) are always correct, but those formed from the product of the polynomials are correct only to a limited degree in .
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Solution
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Part (a)
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Obtain the Maclaurin polynomials and
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Write each function and .
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Context Panel: Series≻Series≻
Complete the Series dialog as per Figure 8.5.17(a).
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Context Panel: Assign to a Name≻p[1] or p[2]
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Figure 8.5.17(a) Series dialogc
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Part (b)
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Form the (sorted) product
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Although the expanded product can be obtained via the Context Panel, the sort option in the Context Panel does not provide for sorting with the powers ascending. Hence, the sort and expand commands have been applied directly.
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Part (c)
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Obtain the degree 11 Maclaurin polynomial for the product
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Write the product , being sure to use the exponential "e" taken from one of the palettes, or from Command Completion.
Context Panel: Series≻Series≻ (See Figure 8.5.17(a) for guidance completing the Series dialog.)
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Part (d)
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Form the Cauchy product of the coefficients of the series for and
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To obtain expressions for the coefficients of the series for and , obtain their formal power series.
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Write , being sure to use Maple's exponential "e".
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Context Panel: Series≻Formal Power Series
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Context Panel: Series≻Formal Power Series
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Write the series for as so that the powers in the series for both and agree.
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Write and as Maple functions
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Write
Context Panel: Assign Function
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Write
Context Panel: Assign Function
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Form , the coefficient of the Cauchy product, as a Maple function
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Write
Context Panel: Assign Function
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Display a sequence of coefficients
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Write
Context Panel: Sequence≻
Complete the Sequence dialog as per Figure 8.5.17(b)ib
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Context Panel: Sequence≻
Complete the Sequence dialog as per Figure 8.5.17(b)
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Context Panel: Simplify≻Simplify
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Figure 8.5.17(b) Sequence dialog
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Part (e)
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The coefficients formed via the Cauchy product are all correct, as a comparison with the Maclaurin series for the product shows. However, the coefficients in the product of are correct only up to the term of degree 8. When multiplying Taylor or Maclaurin polynomials, care should be taken with respect to the degree of the polynomials. Not all the terms in the finite product will be correct.
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