Skills Review for Arc Length and Curvature

Learning Outcomes

  • Use the Fundamental Theorem of Calculus, Part 2, to evaluate definite integrals
  • Use a table of integrals to solve integration problems

In the Arc Length and Curvature section, we will explore the curvature of vector-valued functions. Here we will review how to apply the Second Fundamental Theorem of Calculus and use integration table formulas.

Fundamental Theorem of Calculus, Part 2: The Evaluation Theorem

The Fundamental Theorem of Calculus, Part 2 (also known as the evaluation theorem) states that if we can find an antiderivative for the integrand, then we can evaluate the definite integral by evaluating the antiderivative at the endpoints of the interval and subtracting.

The Fundamental Theorem of Calculus, Part 2


If [latex]f[/latex] is continuous over the interval [latex]\left[a,b\right][/latex] and [latex]F(x)[/latex] is any antiderivative of [latex]f(x),[/latex] then

[latex]{\displaystyle\int }_{a}^{b}f(x)dx=F(b)-F(a)[/latex]

 

Example: Evaluating an Integral with the Fundamental Theorem of Calculus

Use the second part of the Fundamental Theorem of Calculus to evaluate

[latex]{\displaystyle\int }_{-2}^{2}({t}^{2}-4)dt.[/latex]

Example: Evaluating a Definite Integral Using the Fundamental Theorem of Calculus, Part 2

Evaluate the following integral using the Fundamental Theorem of Calculus, Part 2:

[latex]{\displaystyle\int }_{1}^{9}\dfrac{x-1}{\sqrt{x}}dx.[/latex]

Try It

Use the second part of the Fundamental Theorem of Calculus to evaluate [latex]{\displaystyle\int }_{1}^{2}{x}^{-4}dx.[/latex]

Try It

Tables of Integrals

Integration tables, if used in the right manner, can be a handy way either to evaluate or check an integral quickly. Keep in mind that when using a table to check an answer, it is possible for two completely correct solutions to look very different. For example, in Trigonometric Substitution, we found that, by using the substitution [latex]x=\tan\theta[/latex], we can arrive at

[latex]\displaystyle\int \frac{dx}{\sqrt{1+{x}^{2}}}=\text{ln}\left(x+\sqrt{{x}^{2}+1}\right)+C[/latex].

 

However, using [latex]x=\text{sinh}\theta[/latex], we obtained a different solution—namely,

[latex]\displaystyle\int \frac{dx}{\sqrt{1+{x}^{2}}}={\text{sinh}}^{-1}x+C[/latex].

 

We later showed algebraically that the two solutions are equivalent. That is, we showed that [latex]{\text{sinh}}^{-1}x=\text{ln}\left(x+\sqrt{{x}^{2}+1}\right)[/latex]. In this case, the two antiderivatives that we found were actually equal. This need not be the case. However, as long as the difference in the two antiderivatives is a constant, they are equivalent.

Example: Using a Formula from a Table to Evaluate an Integral

Use the table formula

[latex]\displaystyle\int \frac{\sqrt{{a}^{2}-{u}^{2}}}{{u}^{2}}du=-\frac{\sqrt{{a}^{2}-{u}^{2}}}{u}-{\sin}^{-1}\frac{u}{a}+C[/latex]

 

to evaluate [latex]\displaystyle\int \frac{\sqrt{16-{e}^{2x}}}{{e}^{x}}dx[/latex].

The full integration table with formulas can be found in Appendix A.