Series Representations of Functions (College Board AP® Calculus BC): Exam Questions

1 hour37 questions
1
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2 marks

The function f has derivatives of all orders for all real numbers. It is known that f open parentheses 0 close parentheses equals 6, f apostrophe open parentheses 0 close parentheses equals 1, f to the power of apostrophe apostrophe end exponent open parentheses 0 close parentheses equals negative 18, and f to the power of apostrophe apostrophe apostrophe end exponent open parentheses 0 close parentheses equals 3. Write the third-degree Taylor polynomial for f about x equals 0 and use it to approximate the value of f open parentheses 1 close parentheses.

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2
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1 mark

The Maclaurin series for the exponential function e to the power of x is

e to the power of x space equals space 1 plus x plus fraction numerator x squared over denominator 2 factorial end fraction plus fraction numerator x cubed over denominator 3 factorial end fraction plus... plus fraction numerator x to the power of n over denominator n factorial end fraction plus...

Let f be the function defined by f open parentheses x close parentheses equals e to the power of negative 4 x end exponent. Write the third-degree Taylor polynomial for f about x equals 0.

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3a
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3 marks

A function f is given in power series form as f open parentheses x close parentheses equals sum from n equals 1 to infinity of fraction numerator open parentheses negative 1 close parentheses to the power of n times x to the power of n over denominator 4 to the power of n times n end fraction.

Use the ratio test to determine the radius of convergence of the series.

3b
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2 marks

By testing the endpoints, determine the full interval of convergence for f open parentheses x close parentheses. Show the work that leads to your answer.

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4
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3 marks

A function f is given in power series form as f open parentheses x close parentheses equals sum from n equals 1 to infinity of fraction numerator open parentheses negative 1 close parentheses to the power of n times x to the power of n over denominator 5 to the power of n end fraction.

Show that the power series is a geometric series, and hence determine the interval of convergence for f open parentheses x close parentheses.

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5a
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2 marks

The function f is defined by f open parentheses x close parentheses equals fraction numerator 1 over denominator 1 plus x squared end fraction. Find f apostrophe open parentheses x close parentheses.

5b
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2 marks

The Maclaurin series for f is given by 1 minus x squared plus x to the power of 4 minus x to the power of 6 plus... plus open parentheses negative 1 close parentheses to the power of n x to the power of 2 n end exponent+..., which converges to f open parentheses x close parentheses for negative 1 less than x less than 1.

Find the first three nonzero terms and the general term for the Maclaurin series for f to the power of apostrophe open parentheses x close parentheses.

5c
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1 mark

Use your results from parts (a) and (b) to find the sum of the infinite series negative 2 over 3 plus 4 over 3 cubed minus 6 over 3 to the power of 5 plus... plus open parentheses negative 1 close parentheses to the power of n fraction numerator 2 n over denominator 3 to the power of 2 n minus 1 end exponent end fraction plus....

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1a
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2 marks
A graph of function f on axes labelled from -3 to 5 on the x-axis and -4 to 5 on the y-axis. The tangent line to f at the point (0, 2) is also shown, which also goes through the point (1, -2)

The function f has derivatives of all orders for all real numbers x. A portion of the graph of f is shown above, including the tangent line to the graph of f at x equals 0. Selected derivatives for f at x equals 0 are given in the table below.

bold italic n

Error converting from MathML to accessible text.

2

negative 15

3

147

4

negative 9274 over 5

Write the third-degree Taylor polynomial for f about x equals 0.

1b
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2 marks

Write the first three nonzero terms of the Taylor series for e to the power of x about x equals 0. Write the second-degree Taylor polynomial for e to the power of x f open parentheses x close parentheses about x equals 0.

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2
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3 marks

The function f has derivatives of all orders for all real numbers. It is known that f open parentheses 0 close parentheses equals 4 and f apostrophe open parentheses 0 close parentheses equals negative 3.

Let g be the function such that g open parentheses 0 close parentheses equals 5 and g to the power of apostrophe open parentheses x close parentheses equals e to the power of 2 x end exponent times f open parentheses x close parentheses. Write the second-degree Taylor polynomial for g about x equals 0.

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3a
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2 marks

The Taylor series for ln open parentheses 1 plus x close parentheses about x equals 0 is given by

x minus x squared over 2 plus x cubed over 3 minus x to the power of 4 over 4 plus... plus fraction numerator open parentheses negative 1 close parentheses to the power of n plus 1 end exponent x to the power of n over denominator n end fraction plus...,

which converges to ln open parentheses 1 plus x close parentheses on its interval of convergence.

Let f be the function defined by f open parentheses x close parentheses equals x squared ln open parentheses 1 plus x over 2 close parentheses space.

Write the first four nonzero terms and the general term of the Taylor series for f about x equals 0.

3b
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5 marks

Determine the interval of convergence of the Taylor series for f about x equals 0. Show the work that leads to your answer.

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4
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3 marks

The Taylor series for a function f about x equals 2 is given by sum from n equals 1 to infinity of open parentheses negative 1 close parentheses to the power of n plus 1 end exponent fraction numerator 3 to the power of n over denominator 2 n end fraction open parentheses x minus 2 close parentheses to the power of n. Find the first three nonzero terms and the general term of the Taylor series for f apostrophe, the derivative of f, about x equals 2.

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5
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2 marks

The Maclaurin series for a function f is given by f open parentheses x close parentheses equals sum from n equals 0 to infinity of fraction numerator open parentheses negative 1 close parentheses to the power of n open parentheses 2 x close parentheses to the power of 2 n end exponent over denominator open parentheses 2 n close parentheses factorial end fraction equals 1 minus 2 x squared plus fraction numerator 2 x to the power of 4 over denominator 3 end fraction minus fraction numerator 4 x to the power of 6 over denominator 45 end fraction plus..., which converges for all real numbers x. If the first three nonzero terms of the series are used to approximate f open parentheses x close parentheses on the interval space minus 1 half less or equal than x less or equal than 1 third, use the alternating series error bound to determine an upper bound for the error of the approximations.

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6
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2 marks

A function f has derivatives of all orders for all real numbers x. The fourth-degree Taylor polynomial for f about x equals 2 is used to approximate f open parentheses 1.9 close parentheses. Given that open vertical bar f to the power of open parentheses 5 close parentheses end exponent open parentheses x close parentheses close vertical bar less or equal than 9 for 1.5 less or equal than x less or equal than 2, use the Lagrange error bound to show that this approximation is within 1 over 10 to the power of 6 of the exact value of f open parentheses 1.9 close parentheses.

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1
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2 marks

Let y equals f open parentheses x close parentheses be the particular solution to the differential equation fraction numerator d y over denominator d x end fraction equals 2 x squared y times ln x with the initial condition f open parentheses 1 close parentheses equals 5. It can be shown that f to the power of apostrophe apostrophe end exponent open parentheses 1 close parentheses equals 10.

Write the second-degree Taylor polynomial for f about x equals 1, and use the polynomial to approximate f open parentheses 2 close parentheses.

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2
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5 marks

The function f has derivatives of all orders for all real numbers. It is known that f open parentheses 0 close parentheses equals 3, f apostrophe open parentheses 0 close parentheses equals negative 2, and f to the power of apostrophe apostrophe end exponent open parentheses x close parentheses equals f open parentheses 2 x squared close parentheses. Write the fourth-degree Taylor polynomial for f about x equals 0. Show the work that leads to your answer.

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3
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4 marks

A function f is such that f open parentheses 3 close parentheses equals 2 and the Taylor series of its derivative f to the power of apostrophe is given by space f to the power of apostrophe open parentheses x close parentheses equals sum from n equals 1 to infinity of open parentheses negative 1 close parentheses to the power of n plus 1 end exponent 5 to the power of n open parentheses x minus 3 close parentheses to the power of n minus 1 end exponent. Use this function to determine f explicitly within the radius of convergence of the series.

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4a4 marks

The Maclaurin series for a function f is given by f open parentheses x close parentheses equals x squared minus x to the power of 4 over 2 plus x to the power of 6 over 3 minus x to the power of 8 over 4 plus... plus open parentheses negative 1 close parentheses to the power of n plus 1 end exponent times x to the power of 2 n end exponent over n plus..., which converges on open square brackets negative 1 comma space 1 close square brackets.

Write the first four nonzero terms of the Maclaurin series for f to the power of apostrophe open parentheses t to the power of 4 close parentheses. Given that g open parentheses x close parentheses equals integral subscript 0 superscript x f to the power of apostrophe open parentheses t to the power of 4 close parentheses space d t, use the first two nonzero terms of the Maclaurin series for g to approximate g open parentheses 1 close parentheses.

4b
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3 marks

Show that your approximation in part (a) must differ from g open parentheses 1 close parentheses by less than 1 over 10. Justify your answer.

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5
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3 marks

Let the function f be defined by f open parentheses x close parentheses equals ln open parentheses 1 plus 2 x squared close parentheses. The Taylor series for f about x equals 0 is given by sum from n equals 1 to infinity of open parentheses negative 1 close parentheses to the power of n plus 1 end exponent fraction numerator 2 to the power of n x to the power of 2 n end exponent over denominator n end fraction, which converges on the interval open square brackets negative fraction numerator 1 over denominator square root of 2 end fraction comma space fraction numerator 1 over denominator square root of 2 end fraction close square brackets. Use the Taylor series to find a rational number A such that open vertical bar A minus ln open parentheses 3 over 2 close parentheses close vertical bar less than 1 over 50. Justify your answer.

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6
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4 marks

Let the function f be defined by f open parentheses x close parentheses equals sin open parentheses 3 x close parentheses. The fourth-degree Taylor polynomial for f about x equals 1 is used to approximate f open parentheses x close parentheses. Use the Lagrange error bound to show that this approximation will be within 7 over 10 to the power of 4 of the exact value of f open parentheses x close parentheses for all x in the interval 0.8 less or equal than x less or equal than 1.2.

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7
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4 marks

For a function f, the Maclaurin series is given by f open parentheses x close parentheses equals sum from n equals 4 to infinity of fraction numerator open parentheses negative 1 close parentheses to the power of n plus 1 end exponent over denominator n minus 1 end fraction times open parentheses x over 3 close parentheses to the power of n. For open vertical bar x close vertical bar less than R, where R is the radius of convergence of the series, show that y equals f open parentheses x close parentheses is a solution to the differential equation y minus x y apostrophe equals fraction numerator x to the power of 4 over denominator 27 open parentheses x plus 3 close parentheses end fraction.

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