Integrals Resulting in Inverse Trigonometric Functions

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \int\frac{du}{\sqrt{a^2 - u^2}} = \arcsin \left(\frac{u}{a}\right) + C }

$\int {\frac {du}{a^{2}+u^{2}}}={\dfrac {1}{a}}\arctan \left({\dfrac {u}{a}}\right)+C$

$\int {\frac {du}{u{\sqrt {u^{2}-a^{2}}}}}={\frac {1}{a}}\operatorname {arcsec} \left({\dfrac {|u|}{a}}\right)+C$

Example 1

Evaluate the integral

$\int {\dfrac {dx}{\sqrt {4-9x^{2}}}}.$

Solution

Substitute $u=3x$. Then $du=3dx$ and we have

$\int {\dfrac {dx}{\sqrt {4-9x^{2}}}}={\dfrac {1}{3}}\int {\dfrac {du}{\sqrt {4-u^{2}}}}.$

Applying the formula with $a=2,$ we obtain

$\int {\dfrac {dx}{\sqrt {4-9x^{2}}}}={\dfrac {1}{3}}\int {\dfrac {du}{\sqrt {4-u^{2}}}}={\dfrac {1}{3}}\arcsin \left({\dfrac {u}{2}}\right)+C={\dfrac {1}{3}}\arcsin \left({\dfrac {3x}{2}}\right)+C.$

Example 2

Evaluate $\int {\frac {4-x}{\sqrt {16-x^{2}}}}{\text{dx}}$.

Solution

This integral requires two different methods to evaluate it. We get to those methods by splitting up the integral:

$\int {\frac {4-x}{\sqrt {16-x^{2}}}}{\text{dx}}=\int {\frac {4}{\sqrt {16-x^{2}}}}{\text{dx}}-\int {\frac {x}{\sqrt {16-x^{2}}}}{\text{dx}}$

The first integral is handled straightforward; the second integral is handled by substitution, with $u=16-x^{2}$. We handle each separately.

$\int {\frac {4}{\sqrt {16-x^{2}}}}{\text{dx}}=4\arcsin {\frac {x}{4}}+C.$

$\int {\frac {x}{\sqrt {16-x^{2}}}}{\text{dx}}$: Set $u=16-x^{2}$, so ${\text{du}}=-2x{\text{dx}}$ and Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle x\text{dx} = -\text{du} /2} . We have

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \begin{align} \int\frac{x}{\sqrt{16-x^2}}\text{dx} = \int\frac{-\text{du} /2}{\sqrt{u}}\\ = -\frac12\int \frac{1}{\sqrt{u}}\text{du} \\ = - \sqrt{u} + C\\ = -\sqrt{16-x^2} + C.\end{align}}

Combining these together, we have

Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \int \frac{4-x}{\sqrt{16-x^2}}\text{dx} = 4\arcsin\frac x4 + \sqrt{16-x^2}+C.}

Resources

• Integration into Inverse trigonometric functions using Substitution by The Organic Chemistry Tutor

• Integrating using Inverse Trigonometric Functions by patrickJMT

Licensing

Content obtained and/or adapted from:

• Integrals Resulting in Inverse Trigonometric Functions, LibreTexts: Mathematics under a CC BY-SA-NC license