Math Problem Statement

Find the sum to infinity of the series (1 + 2x)^(-1/2).

Solution

The given expression (1+2x)12(1 + 2x)^{-\frac{1}{2}} suggests that you are looking to find the sum to infinity of a series derived from this expression. This is typically done by expanding the expression into a binomial series.

Step-by-Step Solution:

We can express (1+2x)12(1 + 2x)^{-\frac{1}{2}} as a binomial series, but this expansion is valid only when 2x<1|2x| < 1, which implies x<12|x| < \frac{1}{2}. The binomial expansion for (1+u)n(1 + u)^n, where n=12n = -\frac{1}{2} and u=2xu = 2x, is:

(1+2x)12=1+(121)(2x)+(122)(2x)2+(123)(2x)3+(1 + 2x)^{-\frac{1}{2}} = 1 + \binom{-\frac{1}{2}}{1}(2x) + \binom{-\frac{1}{2}}{2}(2x)^2 + \binom{-\frac{1}{2}}{3}(2x)^3 + \dots

The general binomial coefficient for negative powers is:

(nk)=n(n1)(n2)...(nk+1)k!\binom{n}{k} = \frac{n(n-1)(n-2)...(n-k+1)}{k!}

For n=12n = -\frac{1}{2}, the first few terms of the series expansion will look like:

(1+2x)12=1x+32x252x3+(1 + 2x)^{-\frac{1}{2}} = 1 - x + \frac{3}{2}x^2 - \frac{5}{2}x^3 + \dots

Sum to Infinity

The infinite series derived from this expansion is:

1x+32x252x3+1 - x + \frac{3}{2}x^2 - \frac{5}{2}x^3 + \dots

This is the binomial series expansion of (1+2x)12(1 + 2x)^{-\frac{1}{2}}. The sum of this series continues indefinitely, but the series is convergent only for x<12|x| < \frac{1}{2}.

Would you like further details or clarifications? Here are some related questions:

  1. How does the binomial theorem apply to negative or fractional powers?
  2. What are the conditions for the convergence of a binomial series?
  3. How would you expand the expression for a different value of nn?
  4. Can you apply this approach to other functions, like (1x)12(1 - x)^{-\frac{1}{2}}?
  5. How do you compute the individual binomial coefficients for negative powers?

Tip: When dealing with binomial expansions for fractional exponents, always check the conditions for convergence, typically related to the absolute value of the variable being less than 1 for the series to converge.

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Math Problem Analysis

Mathematical Concepts

Algebra
Series
Binomial Expansion
Calculus

Formulas

Binomial series expansion for (1 + u)^n
General term for binomial coefficient for negative powers: C(n, k) = n(n-1)(n-2)...(n-k+1)/k!

Theorems

Binomial Theorem for negative or fractional powers

Suitable Grade Level

Grades 11-12