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Find the integral $\int\frac{4x^2+6}{x^3+3x}dx$

Step-by-step Solution

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Final Answer

$2\ln\left(x\right)+\ln\left(x^2+3\right)+C_0$
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Step-by-step Solution

Specify the solving method

1

Rewrite the expression $\frac{4x^2+6}{x^3+3x}$ inside the integral in factored form

$\int\frac{4x^2+6}{x\left(x^2+3\right)}dx$
2

Rewrite the fraction $\frac{4x^2+6}{x\left(x^2+3\right)}$ in $2$ simpler fractions using partial fraction decomposition

$\frac{4x^2+6}{x\left(x^2+3\right)}=\frac{A}{x}+\frac{Bx+C}{x^2+3}$
3

Find the values for the unknown coefficients: $A, B, C$. The first step is to multiply both sides of the equation from the previous step by $x\left(x^2+3\right)$

$4x^2+6=x\left(x^2+3\right)\left(\frac{A}{x}+\frac{Bx+C}{x^2+3}\right)$
4

Multiplying polynomials

$4x^2+6=\frac{x\left(x^2+3\right)A}{x}+\frac{x\left(x^2+3\right)\left(Bx+C\right)}{x^2+3}$
5

Simplifying

$4x^2+6=\left(x^2+3\right)A+x\left(Bx+C\right)$
6

Assigning values to $x$ we obtain the following system of equations

$\begin{matrix}6=3A&\:\:\:\:\:\:\:(x=0) \\ 42=12A+9B-3C&\:\:\:\:\:\:\:(x=-3) \\ 42=12A+9B+3C&\:\:\:\:\:\:\:(x=3)\end{matrix}$
7

Proceed to solve the system of linear equations

$\begin{matrix}3A & + & 0B & + & 0C & =6 \\ 12A & + & 9B & - & 3C & =42 \\ 12A & + & 9B & + & 3C & =42\end{matrix}$
8

Rewrite as a coefficient matrix

$\left(\begin{matrix}3 & 0 & 0 & 6 \\ 12 & 9 & -3 & 42 \\ 12 & 9 & 3 & 42\end{matrix}\right)$
9

Reducing the original matrix to a identity matrix using Gaussian Elimination

$\left(\begin{matrix}1 & 0 & 0 & 2 \\ 0 & 1 & 0 & 2 \\ 0 & 0 & 1 & 0\end{matrix}\right)$
10

The integral of $\frac{4x^2+6}{x\left(x^2+3\right)}$ in decomposed fraction equals

$\int\left(\frac{2}{x}+\frac{2x}{x^2+3}\right)dx$
11

Simplify the expression inside the integral

$\int\frac{2}{x}dx+2\int\frac{x}{x^2+3}dx$
12

Rewrite the fraction $\frac{x}{x^2+3}$ inside the integral as the product of two functions: $x\frac{1}{x^2+3}$

$\int\frac{2}{x}dx+2\int x\frac{1}{x^2+3}dx$
13

We can solve the integral $\int x\frac{1}{x^2+3}dx$ by applying integration by parts method to calculate the integral of the product of two functions, using the following formula

$\displaystyle\int u\cdot dv=u\cdot v-\int v \cdot du$
14

First, identify $u$ and calculate $du$

$\begin{matrix}\displaystyle{u=x}\\ \displaystyle{du=dx}\end{matrix}$
15

Now, identify $dv$ and calculate $v$

$\begin{matrix}\displaystyle{dv=\frac{1}{x^2+3}dx}\\ \displaystyle{\int dv=\int \frac{1}{x^2+3}dx}\end{matrix}$
16

Solve the integral

$v=\int\frac{1}{x^2+3}dx$
17

Solve the integral by applying the formula $\displaystyle\int\frac{x'}{x^2+a^2}dx=\frac{1}{a}\arctan\left(\frac{x}{a}\right)$

$\frac{1}{\sqrt{3}}\arctan\left(\frac{x}{\sqrt{3}}\right)$
18

Now replace the values of $u$, $du$ and $v$ in the last formula

$\int\frac{2}{x}dx+2\left(\frac{\sqrt{3}}{3}x\arctan\left(\frac{x}{\sqrt{3}}\right)-\frac{\sqrt{3}}{3}\int\arctan\left(\frac{x}{\sqrt{3}}\right)dx\right)$
19

Multiply the single term $2$ by each term of the polynomial $\left(\frac{\sqrt{3}}{3}x\arctan\left(\frac{x}{\sqrt{3}}\right)-\frac{\sqrt{3}}{3}\int\arctan\left(\frac{x}{\sqrt{3}}\right)dx\right)$

$\int\frac{2}{x}dx+\frac{2\sqrt{3}}{3}x\arctan\left(\frac{x}{\sqrt{3}}\right)-\frac{2\sqrt{3}}{3}\int\arctan\left(\frac{x}{\sqrt{3}}\right)dx$
20

The integral $\int\frac{2}{x}dx$ results in: $2\ln\left(x\right)$

$2\ln\left(x\right)$
21

The integral $-\frac{2\sqrt{3}}{3}\int\arctan\left(\frac{x}{\sqrt{3}}\right)dx$ results in: $-\frac{2\sqrt{3}}{3}x\arctan\left(\frac{x}{\sqrt{3}}\right)+\ln\left(x^2+3\right)$

$-\frac{2\sqrt{3}}{3}x\arctan\left(\frac{x}{\sqrt{3}}\right)+\ln\left(x^2+3\right)$
22

Gather the results of all integrals

$2\ln\left(x\right)+\frac{2\sqrt{3}}{3}x\arctan\left(\frac{x}{\sqrt{3}}\right)+\ln\left(x^2+3\right)-\frac{2\sqrt{3}}{3}x\arctan\left(\frac{x}{\sqrt{3}}\right)$
23

Cancel like terms $\frac{2\sqrt{3}}{3}x\arctan\left(\frac{x}{\sqrt{3}}\right)$ and $-\frac{2\sqrt{3}}{3}x\arctan\left(\frac{x}{\sqrt{3}}\right)$

$2\ln\left(x\right)+\ln\left(x^2+3\right)$
24

As the integral that we are solving is an indefinite integral, when we finish integrating we must add the constant of integration $C$

$2\ln\left(x\right)+\ln\left(x^2+3\right)+C_0$

Final Answer

$2\ln\left(x\right)+\ln\left(x^2+3\right)+C_0$

Explore different ways to solve this problem

Solving a math problem using different methods is important because it enhances understanding, encourages critical thinking, allows for multiple solutions, and develops problem-solving strategies. Read more

Solve integral of ((4x^2+6)/(x^3+3x))dx using partial fractionsSolve integral of ((4x^2+6)/(x^3+3x))dx using basic integralsSolve integral of ((4x^2+6)/(x^3+3x))dx using u-substitutionSolve integral of ((4x^2+6)/(x^3+3x))dx using trigonometric substitution

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Plotting: $2\ln\left(x\right)+\ln\left(x^2+3\right)+C_0$

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a
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u
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x
y
z
.
(◻)
+
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◻/◻
/
÷
2

e
π
ln
log
log
lim
d/dx
Dx
|◻|
θ
=
>
<
>=
<=
sin
cos
tan
cot
sec
csc

asin
acos
atan
acot
asec
acsc

sinh
cosh
tanh
coth
sech
csch

asinh
acosh
atanh
acoth
asech
acsch

How to improve your answer:

Main Topic: Integrals by Partial Fraction Expansion

The partial fraction decomposition or partial fraction expansion of a rational function is the operation that consists in expressing the fraction as a sum of a polynomial (possibly zero) and one or several fractions with a simpler denominator.

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