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    IB Math AAHL
    /
    Maclaurin
    /

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    Maclaurin

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    Maclaurin Series Basics

    7 skills
    General formula
    AHL 5.19

    Maclaurin series allow us to approximate arbitrary functions as polynomials.


    The Maclaurin series for a function f is given by

    f(x)=f(0)+xfβ€²(0)+2!x2​fβ€²β€²(0)+β‹―πŸ“–


    In summation form:

    f(x)=n=0βˆ‘βˆžβ€‹n!f(n)(0)xnβ€‹πŸš«


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    e^x
    AHL 5.19

    The Maclaurin series for ex is

    ex=1+x+2!x2​+β‹―πŸ“–
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    sin(x)
    AHL 5.19

    The Maclaurin series for sinx is

    sinx=xβˆ’3!x3​+5!x5β€‹βˆ’β‹―πŸ“–
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    cos(x)
    AHL 5.19

    The Maclaurin series for cosx is

    cosx=1βˆ’2!x2​+4!x4β€‹βˆ’β‹―πŸ“–
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    ln(x+1)
    AHL 5.19

    The Maclaurin series for ln(x+1) is

    ln(x+1)=xβˆ’2x2​+3x3β€‹βˆ’β‹―πŸ“–
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    arctan(x)
    AHL 5.19

    The Maclaurin series for arctanx is

    arctanx=xβˆ’3x3​+5x5β€‹βˆ’β‹―πŸ“–
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    Binomial extension for rational exponents
    AHL AA 1.10

    The binomial theorem can be extended to expansions with rational exponents (n∈Q):

    (a+b)n=an(1+n(ab​)+2!n(nβˆ’1)​(ab​)2+β‹―)πŸ“–
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    Operations on Maclaurin Series

    7 skills
    Maclaurin Series of Composite Functions
    AHL 5.19

    The Maclaurin series for a composite function f(g(x)) is

    f(g(x))=f(0)+g(x)fβ€²(0)+2![g(x)]2​fβ€²β€²(0)🚫


    Basically, we replace xn with [g(x)]n.

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    Adding and Subtracting Series
    AHL 5.19

    We can add or subtract Maclaurin polynomials by adding or subtracting the coefficients of each power of x from the original polynomials.

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    Integration of Maclaurin Series
    AHL 5.19

    We can integrate a function by integrating its Maclaurin polynomial term by term.

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    Differentiation of Maclaurin Series
    AHL 5.19

    We can differentiate a Maclaurin series using the power rule on each term.

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    Multiplying Maclaurin Series
    AHL 5.19

    We can find the first few terms in the Maclaurin Series for a product f(x)Γ—g(x) by multiplying out the first few terms in the Maclaurin Series for f and g.

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    Division of Maclaurin Series
    AHL 5.19

    We can perform "division" of Maclaurin series by assuming that the result of the division is a series with

    p(x)=g(x)f(x)​=a0​+a1​x+a2​x2+β‹―,

    where an​ are the coefficients of the nth power term. Then, we multiply g(x)f(x)​ and a0​+a1​x+a2​x2+... by g(x). Finally, we solve for the unknown coefficients using the Maclaurin series of f(x).

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    Limits using Maclaurin Series
    AHL 5.19

    Certain limits may be evaluated with L’HΓ΄pital's rule but require difficult or repeated differentiation. Sometimes, expanding a function within the limit using its Maclaurin series and simplifying is an easier method for evaluating these limits.


    This kind of simplification often works because we know that after a certain point, every term will tend to 0, allowing us to focus on the few terms that do not.