Question

Determine the Maclaurin series expansion for $$ f(x)=\frac{1}{1+x} $$.

Short answer

Answer: The Maclaurin series expansion for the function \(f(x) = \frac{1}{1+x}\) is \(f(x) = \sum_{n=0}^{\infty} (-x)^n\).

Step-by-step solution

Geometric series formula for f(x)

Recall that the geometric series formula is given by: $$ \frac{1}{1-x} = 1 + x + x^2 + x^3 + \cdots = \sum_{n=0}^{\infty} x^n $$ We can use this formula by replacing x with -x to find the Maclaurin series for the given function: $$ f(x) = \frac{1}{1+x} = \frac{1}{1-(-x)} $$

Apply the geometric series formula

Applying the geometric series formula, we get: $$ f(x) = 1 - x + x^2 - x^3 + \cdots = \sum_{n=0}^{\infty} (-x)^n $$

Conclusion

The Maclaurin series expansion for the function \(f(x) = \frac{1}{1+x}\) is: $$ f(x) = \sum_{n=0}^{\infty} (-x)^n $$

Key concepts

Geometric Series Formula

Understanding the geometric series formula is crucial when dealing with mathematical series, especially when we aim to find patterns that simplify complex functions. Imagine you have a repeating pattern where each term is a constant multiple of the previous term—this scenario is where the geometric series shines. For instance, a series like \(1, r, r^2, r^3, ...\text{,}\) where each term after the first is multiplied by a common ratio \(r\text{,}\) forms a geometric progression.

Mathematically, we can sum the terms of a geometric series using the formula:\[\frac{1}{1 - r} = 1 + r + r^2 + r^3 + \cdots\]where \(r\) is the common ratio, and the series converges if \(|r| < 1\text{.}\) This is a powerful tool because it allows us to transform functions into an infinite series of powers, which not only simplifies calculations but also provides insights into the behavior of functions around certain points, such as \(x = 0\) in the case of the Maclaurin series expansion.

Infinite Series

In the world of calculus and higher mathematics, an infinite series is a sequence of numbers added indefinitely. Such series can sometimes approach a finite limit, which is a concept known as convergence. One classic example of an infinite series is the geometric series mentioned earlier. However, just because a series is infinite doesn't always mean it's solvable or meaningful; some infinite series diverge, which means they grow without bounds as we add more terms.

Mathematicians have developed tests to determine the convergence or divergence of these series. When dealing with the Maclaurin series, as in our exercise, we’re typically looking at an infinite power series. To utilize such series in calculations, we need them to converge, which happens under certain conditions for the input variable \(x\text{.}\) That's also why we often talk about the 'radius of convergence' when discussing power series—within this radius, we can confidently say our series will have a finite sum.

Mathematical Series Convergence

Convergence in mathematical series is a fundamental topic, as it determines whether the series has a meaningful sum when an infinite number of terms are considered. A series converges if its partial sums get closer and closer to a certain number as more terms are added. Conversely, a series diverges if its partial sums fail to approach a single value.

To test for convergence, mathematicians employ various criteria—like the Ratio Test, Root Test, or Comparison Test, among others. The geometric series formula we used in our function \(f(x) = \frac{1}{1+x}\) is a prime example of a convergent series, but only when the absolute value of the common ratio \(r\) is less than one. This property assures us that as \(n\) approaches infinity, the terms of the series approach zero, making the sum finite. It's this concept of convergence that allows us to confidently write down the Maclaurin series expansion for our function and use it for analysis and computation in a variety of mathematical and practical applications.