Binomial Theorem (DP IB Analysis & Approaches (AA))

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  • What is the binomial theorem?

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  • What is the binomial theorem?

    The binomial theorem is a method for expanding a two-term expression in a bracket raised to a power, e.g. open parentheses a plus b close parentheses to the power of n.

  • True or False?

    The binomial theorem only applies to linear expressions.

    False.

    The binomial theorem applies to any two-term expression, but in IB it is most often applied to linear expressions.

  • State the equation for the binomial theorem.

    The equation for the binomial theorem is open parentheses a plus b close parentheses to the power of n equals a to the power of n plus scriptbase straight C subscript 1 end scriptbase presubscript blank presuperscript n space a to the power of n italic minus italic 1 end exponent b plus... plus scriptbase straight C subscript r end scriptbase presubscript blank presuperscript n space a to the power of n minus r end exponent b to the power of r plus... plus b to the power of n

    Where:

    • scriptbase straight C subscript r end scriptbase presubscript blank presuperscript n equals fraction numerator n factorial over denominator r factorial open parentheses n minus r close parentheses factorial end fraction

    This equation is valid for any n element of straight natural numbers (i.e., n equals 0 comma space 1 comma space 2 comma space 3 comma space...).

    The equation is in the exam formula booklet.

  • What is the binomial coefficient?

    The binomial coefficient scriptbase straight C subscript r end scriptbase presubscript blank presuperscript n is used to find the coefficients in a binomial expansion.

    Its value is given by scriptbase straight C subscript r end scriptbase presubscript blank presuperscript n equals fraction numerator n factorial over denominator r factorial open parentheses n minus r close parentheses factorial end fraction, which is in the exam formula booklet (although you will usually use your GDC to find the value of the coefficients in an expansion).

    scriptbase straight C subscript r end scriptbase presubscript blank presuperscript n also represents the number of ways to choose r items out of n different items.

  • True or False?

    Binomial coefficients are always integers.

    True.

    Binomial coefficients are always integers.

  • True or False?

    Pascal's triangle can be used to find binomial coefficients scriptbase straight C subscript r end scriptbase presubscript blank presuperscript n.

    True.

    Pascal's triangle is a triangular array of the binomial coefficients, and can be used to find scriptbase straight C subscript r end scriptbase presubscript blank presuperscript n for different values of n and r.

    However Pascal's triangle becomes awkward to use when n gets large.

  • True or False?

    In Pascal's triangle, each number is the sum of the two numbers directly above it.

    True.

    In Pascal's triangle, each number is the sum of the two numbers directly above it.

  • True or False?

    scriptbase straight C subscript r end scriptbase presubscript blank presuperscript n equals scriptbase straight C subscript n minus r end subscript end scriptbase presubscript blank presuperscript n

    True.

    scriptbase straight C subscript r end scriptbase presubscript blank presuperscript n equals scriptbase straight C subscript n minus r end subscript end scriptbase presubscript blank presuperscript n

    E.g. scriptbase straight C subscript 2 end scriptbase presubscript blank presuperscript 7 equals scriptbase straight C subscript 5 end scriptbase presubscript blank presuperscript 7

  • What does the ellipsis (...) indicate in a binomial expansion?

    The ellipsis (...) in a binomial expansion indicates that the expansion continues.

  • What does 'in ascending powers' mean?

    'In ascending powers' means that the terms are arranged so that the power of the variable increases with each term.

  • True or False?

    The binomial theorem can be applied to negative and fractional indices.

    True.

    The binomial theorem can be applied to negative and fractional indices.

  • What is the general form of the binomial expansion for open parentheses a plus b close parentheses to the power of n where n element of straight rational numbers?

    The general form of the binomial expansion for open parentheses a plus b close parentheses to the power of n, where n element of straight rational numbers, is open parentheses a plus b close parentheses to the power of n equals a to the power of n open parentheses 1 plus n open parentheses b over a close parentheses plus fraction numerator n open parentheses n minus 1 close parentheses over denominator 2 factorial end fraction open parentheses b over a close parentheses squared plus horizontal ellipsis close parentheses.

    This is in the exam formula booklet.

  • True or False?

    All binomial expansions of open parentheses a plus b close parentheses to the power of n end after a finite number of terms.

    False.

    Not all binomial expansions of open parentheses a plus b close parentheses to the power of n end after a finite number of terms.

    If n is a positive integer (or zero), then the expansion will end after a finite number of terms.

    If n element of straight rational numbers is not a positive integer (or zero), then the binomial expansion will have an infinite number of terms (it will'go on forever').

  • What is the general form of the binomial expansion for open parentheses 1 plus x close parentheses to the power of n where n element of straight rational numbers?

    The general form of the binomial expansion for open parentheses 1 plus x close parentheses to the power of n, where n element of straight rational numbers, is open parentheses 1 plus x close parentheses to the power of n equals 1 plus n x plus fraction numerator n open parentheses n minus 1 close parentheses over denominator 2 factorial end fraction x squared plus fraction numerator n open parentheses n minus 1 close parentheses open parentheses n minus 2 close parentheses over denominator 3 factorial end fraction x cubed plus horizontal ellipsis.

    The interval of convergence for the expansion is open vertical bar x close vertical bar less than 1.

    This formula is not in the exam formula booklet, but it can be derived from the formula for open parentheses a plus b close parentheses to the power of n which is in the booklet.

  • What does "the interval of convergence" mean for a binomial expansion?

    The interval of convergence is the range of x values for which a binomial expansion is valid.

    E.g. the interval of convergence for fraction numerator 1 over denominator 1 minus x end fraction equals 1 plus x plus x squared plus x cubed plus... is open vertical bar x close vertical bar less than 1 (which can also be written as negative 1 less than x less than 1).

  • What is the interval of convergence for a binomial expansion of open parentheses a plus b x close parentheses to the power of n.

    The interval of convergence for a binomial expansion of open parentheses a plus b x close parentheses to the power of n is negative a over b less than x less than a over b.

  • If you are using the binomial expansion open parentheses 1 minus x close parentheses to the power of 1 half end exponent equals 1 minus x over 2 minus x squared over 8 minus x cubed over 16 minus horizontal ellipsis to approximate the value of square root of 0.97 end root, what value of x should you substitute into the expansion?

    If you are using the binomial expansion open parentheses 1 minus x close parentheses to the power of 1 half end exponent equals 1 minus x over 2 minus x squared over 8 minus x cubed over 16 minus horizontal ellipsis to approximate the value of square root of 0.97 end root, you should substitute the value x equals 0.03 into the expansion.

    Compare the expressions: open parentheses 1 minus x close parentheses to the power of 1 half end exponent equals open parentheses 0.97 close parentheses to the power of 1 half end exponent space rightwards double arrow space 1 minus x equals 0.97 space rightwards double arrow space x equals 0.03.

  • True or False?

    The more terms used in a binomial expansion approximation, the closer the approximation is to the true value.

    True.

    The more terms used in a binomial expansion approximation, the closer the approximation is to the true value.