The error function erf(«) = [e*at is used in probability, statistics, and engineering. (a) Show that e- dt =VTlerf(b) – erf(a)]. (1) erf(x) = dt dt= erf(x) (2) By this property of definite integrals, e dt = dt + dt (1) and (2) = dt dt - dt erf(b) – erf a - ert a (b) Show that the function y = eerf(x) satisfies the differential equation y' = 2xy + 2/VT. y = e*erf(x) = y' = erf(x) + e*erf (x) 2x [by FTC1]

Calculus: Early Transcendentals
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Author:James Stewart
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Chapter1: Functions And Models
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### The Error Function

The error function, denoted as \( \text{erf}(x) \), is defined by the integral:

\[ \text{erf}(x) = \frac{2}{\sqrt{\pi}} \int_{0}^{x} e^{-t^2} dt \]

This function is commonly used in the fields of probability, statistics, and engineering.

### Proofs and Properties

#### (a) Show that:

\[ \int_{a}^{b} e^{-t^2} dt = \frac{1}{2} \sqrt{\pi} [\text{erf}(b) - \text{erf}(a)] \]

1. Given:

\[ \text{erf}(x) = \frac{2}{\sqrt{\pi}} \int_{0}^{x} e^{-t^2} dt \]

We need to show:

\[ \int_{0}^{x} e^{-t^2} dt = \text{erf}(x) \]

However, this should be corrected to:

\[ \int_{0}^{x} e^{-t^2} dt = \frac{\sqrt{\pi}}{2} \text{erf}(x). \]

2. By using the property of definite integrals:

\[ \int_{a}^{b} e^{-t^2} dt = \int_{0}^{b} e^{-t^2} dt - \int_{0}^{a} e^{-t^2} dt \]

Combining (1) and (2), we get:

\[ \int_{a}^{b} e^{-t^2} dt = \frac{\sqrt{\pi}}{2} \left[\text{erf}(b) - \text{erf}(a)\right]. \]

#### (b) Verification of Differential Equation

Show that the function \( y = e^{x^2} \text{erf}(x) \) satisfies the differential equation \( y' = 2xy + \frac{2}{\sqrt{\pi}} \).

Given:

\[ y = e^{x^2} \text{erf}(x) \]

Differentiate \( y \) with respect to \( x \):

\[ y' = \frac{d}{dx} \left(e^{x^2} \text{erf}(x)\right) \]

Using product rule
Transcribed Image Text:### The Error Function The error function, denoted as \( \text{erf}(x) \), is defined by the integral: \[ \text{erf}(x) = \frac{2}{\sqrt{\pi}} \int_{0}^{x} e^{-t^2} dt \] This function is commonly used in the fields of probability, statistics, and engineering. ### Proofs and Properties #### (a) Show that: \[ \int_{a}^{b} e^{-t^2} dt = \frac{1}{2} \sqrt{\pi} [\text{erf}(b) - \text{erf}(a)] \] 1. Given: \[ \text{erf}(x) = \frac{2}{\sqrt{\pi}} \int_{0}^{x} e^{-t^2} dt \] We need to show: \[ \int_{0}^{x} e^{-t^2} dt = \text{erf}(x) \] However, this should be corrected to: \[ \int_{0}^{x} e^{-t^2} dt = \frac{\sqrt{\pi}}{2} \text{erf}(x). \] 2. By using the property of definite integrals: \[ \int_{a}^{b} e^{-t^2} dt = \int_{0}^{b} e^{-t^2} dt - \int_{0}^{a} e^{-t^2} dt \] Combining (1) and (2), we get: \[ \int_{a}^{b} e^{-t^2} dt = \frac{\sqrt{\pi}}{2} \left[\text{erf}(b) - \text{erf}(a)\right]. \] #### (b) Verification of Differential Equation Show that the function \( y = e^{x^2} \text{erf}(x) \) satisfies the differential equation \( y' = 2xy + \frac{2}{\sqrt{\pi}} \). Given: \[ y = e^{x^2} \text{erf}(x) \] Differentiate \( y \) with respect to \( x \): \[ y' = \frac{d}{dx} \left(e^{x^2} \text{erf}(x)\right) \] Using product rule
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