Math Problem Statement

Utilizando series conocidas determine la representacion en serie de potencias de ´ f(x) si:

Utilizando series conocidas determine la representación en serie de potencias de f(x) si: v) f(x) = \int_0^1 e^{-x^2} - 1 \, dx y w) f(x) = \int_0^x e^{-t^2} \, dt.

Solution

The problem requires finding the power series representation of the function f(x)f(x) using known series expansions. The functions are given as:

v)f(x)=01ex21dxv) \quad f(x) = \int_0^1 e^{-x^2} - 1 \, dx w)f(x)=0xet2dtw) \quad f(x) = \int_0^x e^{-t^2} \, dt

Let's begin with v)v) and w)w).

For v)v):

We need to express f(x)=01ex21dxf(x) = \int_0^1 e^{-x^2} - 1 \, dx using a series representation for ex2e^{-x^2}. The Taylor series for ex2e^{-x^2} around x=0x = 0 is:

ex2=n=0(x2)nn!=n=0(1)nx2nn!e^{-x^2} = \sum_{n=0}^{\infty} \frac{(-x^2)^n}{n!} = \sum_{n=0}^{\infty} \frac{(-1)^n x^{2n}}{n!}

Thus, we can rewrite the integrand ex21e^{-x^2} - 1 as:

ex21=n=1(1)nx2nn!e^{-x^2} - 1 = \sum_{n=1}^{\infty} \frac{(-1)^n x^{2n}}{n!}

Now, we integrate term by term from 0 to 1:

f(x)=01n=1(1)nx2nn!dxf(x) = \int_0^1 \sum_{n=1}^{\infty} \frac{(-1)^n x^{2n}}{n!} \, dx

This can be integrated for each term in the series.

For w)w):

The function f(x)=0xet2dtf(x) = \int_0^x e^{-t^2} \, dt involves the Gaussian integral, which does not have a simple closed-form solution. However, we can still expand et2e^{-t^2} in a power series as before:

et2=n=0(1)nt2nn!e^{-t^2} = \sum_{n=0}^{\infty} \frac{(-1)^n t^{2n}}{n!}

Substituting this into the integral:

f(x)=0xn=0(1)nt2nn!dtf(x) = \int_0^x \sum_{n=0}^{\infty} \frac{(-1)^n t^{2n}}{n!} \, dt

Now integrate term by term:

f(x)=n=0(1)nn!0xt2ndt=n=0(1)nn!x2n+12n+1f(x) = \sum_{n=0}^{\infty} \frac{(-1)^n}{n!} \int_0^x t^{2n} \, dt = \sum_{n=0}^{\infty} \frac{(-1)^n}{n!} \cdot \frac{x^{2n+1}}{2n+1}

This is the power series representation for f(x)f(x).


Would you like a more detailed step-by-step solution for the integrals or clarifications on specific parts?

Here are some follow-up questions to consider:

  1. Can you express the final power series for f(x)f(x) in a compact form?
  2. How can you verify the convergence of the series representations?
  3. What is the behavior of f(x)f(x) as x0x \to 0 and xx \to \infty?
  4. How does the series for ex2e^{-x^2} compare to other known expansions, such as sine or cosine?
  5. Can you use the power series to approximate f(x)f(x) for small xx?

Tip: Power series can be a very effective way to approximate functions, especially when the exact integral is difficult to compute.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Power Series
Integration
Taylor Expansion

Formulas

e^{-x^2} = \sum_{n=0}^{\infty} \frac{(-x^2)^n}{n!}
f(x) = \sum_{n=0}^{\infty} \frac{(-1)^n}{n!} \frac{x^{2n+1}}{2n+1}

Theorems

Taylor Series Expansion
Fundamental Theorem of Calculus

Suitable Grade Level

University level (Calculus II or higher)