### Home > APCALC > Chapter 10 > Lesson 10.2.2 > Problem10-126

10-126.

Examine the integrals below. Consider the multiple tools available for integrating and use the best strategy for each part. Evaluate each integral and briefly describe your method. Homework Help ✎

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

You should recognize the integrand as a form of the derivative of $\tan^{–1}(x)$.
The denomintor needs to be of the form $a^2 + 1$.

$\frac{1}{x^2+4}=\frac{1}{4(x^2/4+1)}=\frac{1}{4((x/2)^2+1)}$

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

Use substitution. Let $u = x^2 + 4$.

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

Factor the denominator then use partial fraction decomposition.

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

$\frac{x^2}{x^2+4}=\frac{x^2+4-4}{x^2+4}=1-\frac{4}{x^2+4}$