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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

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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

We can solve the integral $\int\frac{x}{x^2+3}dx$ by applying integration by substitution method (also called U-Substitution). First, we must identify a section within the integral with a new variable (let's call it $u$), which when substituted makes the integral easier. We see that $x^2+3$ it's a good candidate for substitution. Let's define a variable $u$ and assign it to the choosen part

$u=x^2+3$
13

Now, in order to rewrite $dx$ in terms of $du$, we need to find the derivative of $u$. We need to calculate $du$, we can do that by deriving the equation above

$du=2xdx$
14

Isolate $dx$ in the previous equation

$\frac{du}{2x}=dx$
15

Substituting $u$ and $dx$ in the integral and simplify

$\int\frac{2}{x}dx+2\cdot \frac{1}{2}\int\frac{1}{u}du$
16

Multiply $2$ times $\frac{1}{2}$

$\int\frac{2}{x}dx+\int\frac{1}{u}du$
17

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

$2\ln\left(x\right)$
18

The integral $\int\frac{1}{u}du$ results in: $\ln\left(x^2+3\right)$

$\ln\left(x^2+3\right)$
19

Gather the results of all integrals

$2\ln\left(x\right)+\ln\left(x^2+3\right)$
20

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 integration by partsSolve 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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0
a
b
c
d
f
g
m
n
u
v
w
x
y
z
.
(◻)
+
-
×
◻/◻
/
÷
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.

Used Formulas

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