Reversing Derivatives Made Easy: Power Rule of Integration

Definition of the Power Rule for Integration

The power rule states that for any real number \( n \) different from \(-1\), the integral of \( x^n \) with respect to \( x \) is:
\( \int x^n dx = \frac{x^{n+1}}{n+1} + C \)
where \( C \) is the constant of integration.

Why the Exclusion of \( n = -1 \)

The case where \( n = -1 \) is excluded because it leads to the function \( x^{-1} \), which is \( \frac{1}{x} \), and its integral is the natural logarithm function, not a power function. The integral of \( \frac{1}{x} \) is \( \ln|x| + C \).

Applying the Power Rule

General Application: To integrate a function like \( x^3 \), you would apply the power rule as follows:
\( \int x^3 dx = \frac{x^{3+1}}{3+1} + C = \frac{x^4}{4} + C \)

Negative Powers: It also applies to negative powers (except for \(-1\)). For instance:
\( \int x^{-2} dx = \frac{x^{-2+1}}{-2+1} + C = -\frac{1}{x} + C \)

Importance in Calculus

The power rule is a go-to technique for integrating polynomials and any function that can be expressed as a power of \( x \).

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It simplifies the process of finding antiderivatives, which is crucial in solving problems involving areas under curves and in various physical applications.

Limitations

The power rule is not applicable to functions that cannot be expressed as \( x^n \). In such cases, other integration methods like substitution or integration by parts are required.

For \( n = -1 \), a different approach (integration of \( \frac{1}{x} \)) must be used.

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