### Home > CALC > Chapter 12 > Lesson 12.1.2 > Problem12-21

12-21.

Examine the integrals below. Consider the multiple tools available for integrating and use the best strategy. After evaluating each integral, write a short description of your method.

1. $\int \frac { 1 } { x \operatorname { ln } ( 3 x ) } d x$

Use substitution. Let $u = \operatorname{ln}(3x)$.

1. $\int e ^ { x } \operatorname { sin } 2 x d x$

Use integration by parts. Let $f =\operatorname{sin}(2x)$ and $dg = e^xdx$.
Then $df = 2\operatorname{cos}(2x)dx$ and $g = e^x$.

$=e^x\sin(2x)-2\int e^x\cos(2x)dx$

Use integration by parts on the integral in Step 2.
Let $f = \operatorname{cos}(2x)$ and $dg = e^xdx$.
Then $df =-2\operatorname{sin}(2x)dx$ and $g = e^x$.

Use partial fraction decomposition.
$\frac{1}{x^2-x}=\frac{A}{x}+\frac{B}{x-1}$

1. $\int \frac { d x } { x ^ { 2 } - x }$

Use algebra to get the original integral expression by itself.

1. $\int \frac { 1 } { \sqrt { 4 - x ^ { 2 } } } d x$

$\sqrt{4-x^2}=\sqrt{4(1-\frac{x^2}{4})}$

$=2\sqrt{1-\Big(\frac{x}{2}\Big)^2}$

Rewrite the denominator of the integrand using Steps 1 and 2.
You should recognize the integrand as a form of the derivative of a special function.