Question:

Evaluate $\int \frac{x^{2}+4}{x^{4}+16}dx.$

Updated On: Apr 28, 2024
  • $\frac{1}{2\sqrt{2}}\tan^{-1}\left(\frac{x^{2}-4}{2x\sqrt{2}}\right)+c$
  • $\frac{1}{2\sqrt{2}}\tan^{-1}\left(\frac{x^{2}-4}{2\sqrt{2}}\right)+c$
  • $\frac{1}{2\sqrt{2}}\tan^{-1}\left(\frac{x^{2}-4}{x\sqrt{2}}\right)+c$
  • None of the above
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The Correct Option is A

Solution and Explanation

Let $I=\int \frac{x^{2}+4}{x^{4}+16} d x$
$=\int \frac{1+\frac{4}{x^{2}}}{x^{2}+\frac{16}{x^{2}}}$
$d x=\int \frac{1+\frac{4}{x^{2}}}{\left(x-\frac{4}{x}\right)^{2}+8} d x$
Putting $x-\frac{4}{x}=t$
So that $\left(1+\frac{4}{x^{2}}\right) d x=d t$
$\therefore I=\int \frac{d t}{t^{2}+(2 \sqrt{2})^{2}}$
$\Rightarrow \frac{1}{2 \sqrt{2}} \tan ^{-1}\left(\frac{t}{2 \sqrt{2}}\right)+C$
$\Rightarrow I=\frac{1}{2 \sqrt{2}} \tan ^{-1}\left(\frac{x-\frac{4}{x}}{2 \sqrt{2}}\right)+C$
$=\frac{1}{2 \sqrt{2}} \tan ^{-1}\left(\frac{x^{2}-4}{2 x \sqrt{2}}\right)+C$
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Concepts Used:

Integrals of Some Particular Functions

There are many important integration formulas which are applied to integrate many other standard integrals. In this article, we will take a look at the integrals of these particular functions and see how they are used in several other standard integrals.

Integrals of Some Particular Functions:

  • ∫1/(x2 – a2) dx = (1/2a) log|(x – a)/(x + a)| + C
  • ∫1/(a2 – x2) dx = (1/2a) log|(a + x)/(a – x)| + C
  • ∫1/(x2 + a2) dx = (1/a) tan-1(x/a) + C
  • ∫1/√(x2 – a2) dx = log|x + √(x2 – a2)| + C
  • ∫1/√(a2 – x2) dx = sin-1(x/a) + C
  • ∫1/√(x2 + a2) dx = log|x + √(x2 + a2)| + C

These are tabulated below along with the meaning of each part.