Maclaurin Series (DP IB Analysis & Approaches (AA))

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  • What is a Maclaurin series?

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  • What is a Maclaurin series?

    A Maclaurin series is a way of representing a function as an infinite sum of increasing integer powers of x.

    E.g. sin x equals x minus fraction numerator x cubed over denominator 3 factorial end fraction plus fraction numerator x to the power of 5 over denominator 5 factorial end fraction minus horizontal ellipsis

  • What is a truncated Maclaurin series?

    A truncated Maclaurin series is a Maclaurin series that is shortened by stopping at a particular power of x. This provides an approximation of the original function.

  • True or False?

    A truncated Maclaurin series is always exactly equal to the original function for x equals 0 and x equals 1.

    False.

    A truncated Maclaurin series is always exactly equal to the original function for x equals 0.

  • What is the general Maclaurin series formula?

    The general Maclaurin series formula is f open parentheses x close parentheses equals f open parentheses 0 close parentheses plus x f to the power of apostrophe open parentheses 0 close parentheses plus fraction numerator x squared over denominator 2 factorial end fraction f to the power of apostrophe apostrophe end exponent open parentheses 0 close parentheses plus... .

    This is in the exam formula booklet.

  • What is the Maclaurin series expansion for straight e to the power of x?

    The Maclaurin series expansion for straight e to the power of x is straight e to the power of x equals 1 plus x plus fraction numerator x squared over denominator 2 factorial end fraction plus horizontal ellipsis.

    This is in the exam formula booklet.

  • What is the Maclaurin series expansion for ln open parentheses 1 plus x close parentheses?

    The Maclaurin series expansion for ln open parentheses 1 plus x close parentheses is ln open parentheses 1 plus x close parentheses equals x minus x squared over 2 plus x cubed over 3 minus horizontal ellipsis.

    This is in the exam formula booklet.

  • What is the Maclaurin series expansion for sin x?

    The Maclaurin series expansion for sin x is sin x equals x minus fraction numerator x cubed over denominator 3 factorial end fraction plus fraction numerator x to the power of 5 over denominator 5 factorial end fraction minus horizontal ellipsis.

    This is in the exam formula booklet.

  • What is the Maclaurin series expansion for cos x?

    The Maclaurin series expansion for cos x is cos x equals 1 minus fraction numerator x squared over denominator 2 factorial end fraction plus fraction numerator x to the power of 4 over denominator 4 factorial end fraction minus horizontal ellipsis.

    This is in the exam formula booklet.

  • What is the Maclaurin series expansion for arctan x?

    The Maclaurin series expansion for arctan x is arctan x equals x minus x cubed over 3 plus x to the power of 5 over 5 minus horizontal ellipsis.

    This is in the exam formula booklet.

  • How do you find the Maclaurin series for a product of two functions?

    To find the Maclaurin series for a product of two functions:

    • start with the Maclaurin series for the individual functions,

    • put brackets around each series and multiply them together,

    • then collect terms and simplify coefficients.

    How many terms to use for each Maclaurin series will depend on the highest power of x that you need in your final answer.

  • How do you find the Maclaurin series for a composite function?

    To find the Maclaurin series for a composite function:

    • start with the Maclaurin series for the basic 'outside function',

    • substitute the 'inside function' everywhere x appears,

    • then expand and simplify.

  • How can you use a function's Maclaurin series to find the Maclaurin series of the functions' derivative?

    The Maclaurin series of a function's derivative can be found by differentiating the Maclaurin series of the original function term by term.

  • True or False?

    Integrating the Maclaurin series for a derivative f to the power of apostrophe open parentheses x close parentheses gives the Maclaurin series for the function f open parentheses x close parentheses without any additional considerations being required.

    False.

    Integrating the Maclaurin series for a derivative f to the power of apostrophe open parentheses x close parentheses gives the Maclaurin series for the function f open parentheses x close parentheses, but you must also consider the constant of integration.

  • What is the connection between Maclaurin series expansions and binomial theorem series expansions?

    For a function like open parentheses 1 plus x close parentheses to the power of n, the binomial theorem series expansion is exactly the same as the Maclaurin series expansion for the same function.

  • If you have a differential equation in the form fraction numerator straight d y over denominator straight d x end fraction equals g open parentheses x comma space y close parentheses, what other piece of information do you need to know in order to find the Maclaurin series of the solution to the equation?

    If you have a differential equation in the form fraction numerator straight d y over denominator straight d x end fraction equals g open parentheses x comma space y close parentheses, in order to find the Maclaurin series of the solution to the equation you also need to know y open parentheses 0 close parentheses (i.e., the value of y when x is equal to 0).

  • How many derivatives do you need to find when solving a differential equation using Maclaurin series?

    The number of derivatives you need to find when solving a differential equation using Maclaurin series depends on how many terms of the Maclaurin series you want to find.

    For example, for terms up to x to the power of 4, you need to find derivatives up to y to the power of open parentheses 4 close parentheses end exponent.

    (Note: only the complete infinitely-long series gives the exact solution to the differential equation.)

  • What are the steps for finding the Maclaurin series for the solution to a differential equation?

    The steps for finding the Maclaurin series for the solution to a differential equation are:

    1. Use implicit differentiation to find expressions for y to the power of apostrophe apostrophe end exponent comma space y to the power of apostrophe apostrophe apostrophe end exponent comma space y to the power of open parentheses 4 close parentheses end exponent, etc., in terms of x comma space y and lower-order derivatives of y

    2. Use the given initial value for y left parenthesis 0 right parenthesis to find the values of y to the power of apostrophe left parenthesis 0 right parenthesis comma space y to the power of apostrophe apostrophe end exponent left parenthesis 0 right parenthesis comma space y to the power of apostrophe apostrophe apostrophe end exponent left parenthesis 0 right parenthesis comma space y to the power of open parentheses 4 close parentheses end exponent open parentheses 0 close parentheses, etc., one by one. 

    3. Put the values found in step 2 into the general Maclaurin series formula f left parenthesis x right parenthesis equals f left parenthesis 0 right parenthesis plus x f to the power of apostrophe left parenthesis 0 right parenthesis plus fraction numerator x squared over denominator 2 factorial end fraction f to the power of apostrophe apostrophe end exponent left parenthesis 0 right parenthesis plus... (where f open parentheses 0 close parentheses equals y open parentheses 0 close parentheses, f to the power of apostrophe open parentheses 0 close parentheses equals y to the power of apostrophe open parentheses 0 close parentheses, etc.)

    4. Simplify the coefficients for each of the powers of x in the resultant Maclaurin series.

    The general Maclaurin series formula is in the exam formula booklet.

  • True or False?

    A Maclaurin series solution to a differential equation can be used to find approximations of the solution y equals f open parentheses x close parentheses for different values of x, even if the exact solution cannot be found explicitly.

    True.

    A Maclaurin series solution to a differential equation can be used to find approximations of the solution y equals f open parentheses x close parentheses for different values of x, even if the exact solution cannot be found explicitly.

  • True or False?

    The Maclaurin series solution to a differential equation always gives you the explicit function of x that corresponds to the solution.

    False.

    The Maclaurin series solution to a differential equation does not necessarily give you the explicit function of x that corresponds to the solution.

    What it does give you is the exact Maclaurin series of that solution.

  • How can you increase the accuracy of the Maclaurin series approximation for a differential equation solution?

    You can increase the accuracy of the Maclaurin series approximation for a differential equation solution by calculating additional terms of the Maclaurin series for higher powers of x.