👉 Try now NerdPal! Our new math app on iOS and Android

Find the integral $\int\frac{-x^2+8x^2-9x+2}{\left(x^2+1\right)\left(x-3\right)^2}dx$

Step-by-step Solution

Go!
Math mode
Text mode
Go!
1
2
3
4
5
6
7
8
9
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

Final answer to the problem

$\frac{7}{50}\arctan\left(x\right)-\frac{51}{100}\ln\left(x^2+1\right)+\frac{-19}{5\left(x-3\right)}+\frac{51}{50}\ln\left(x-3\right)+C_0$
Got another answer? Verify it here!

Step-by-step Solution

Specify the solving method

1

Combining like terms $-x^2$ and $8x^2$

$\int\frac{7x^2-9x+2}{\left(x^2+1\right)\left(x-3\right)^2}dx$
2

Rewrite the fraction $\frac{7x^2-9x+2}{\left(x^2+1\right)\left(x-3\right)^2}$ in $3$ simpler fractions using partial fraction decomposition

$\frac{7x^2-9x+2}{\left(x^2+1\right)\left(x-3\right)^2}=\frac{Ax+B}{x^2+1}+\frac{C}{\left(x-3\right)^2}+\frac{D}{x-3}$
3

Find the values for the unknown coefficients: $A, B, C, D$. The first step is to multiply both sides of the equation from the previous step by $\left(x^2+1\right)\left(x-3\right)^2$

$7x^2-9x+2=\left(x^2+1\right)\left(x-3\right)^2\left(\frac{Ax+B}{x^2+1}+\frac{C}{\left(x-3\right)^2}+\frac{D}{x-3}\right)$
4

Multiplying polynomials

$7x^2-9x+2=\frac{\left(x^2+1\right)\left(x-3\right)^2\left(Ax+B\right)}{x^2+1}+\frac{\left(x^2+1\right)\left(x-3\right)^2C}{\left(x-3\right)^2}+\frac{\left(x^2+1\right)\left(x-3\right)^2D}{x-3}$
5

Simplifying

$7x^2-9x+2=\left(x-3\right)^2\left(Ax+B\right)+\left(x^2+1\right)C+\left(x^2+1\right)\left(x-3\right)D$
6

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

$\begin{matrix}18=-16A+16B+2C-8D&\:\:\:\:\:\:\:(x=-1) \\ 0=4A+4B+2C-4D&\:\:\:\:\:\:\:(x=1) \\ 38=10C&\:\:\:\:\:\:\:(x=3) \\ 92=-108A+36B+10C-60D&\:\:\:\:\:\:\:(x=-3)\end{matrix}$
7

Proceed to solve the system of linear equations

$\begin{matrix} -16A & + & 16B & + & 2C & - & 8D & =18 \\ 4A & + & 4B & + & 2C & - & 4D & =0 \\ 0A & + & 0B & + & 10C & + & 0D & =38 \\ -108A & + & 36B & + & 10C & - & 60D & =92\end{matrix}$
8

Rewrite as a coefficient matrix

$\left(\begin{matrix}-16 & 16 & 2 & -8 & 18 \\ 4 & 4 & 2 & -4 & 0 \\ 0 & 0 & 10 & 0 & 38 \\ -108 & 36 & 10 & -60 & 92\end{matrix}\right)$
9

Reducing the original matrix to a identity matrix using Gaussian Elimination

$\left(\begin{matrix}1 & 0 & 0 & 0 & -\frac{51}{50} \\ 0 & 1 & 0 & 0 & \frac{7}{50} \\ 0 & 0 & 1 & 0 & \frac{19}{5} \\ 0 & 0 & 0 & 1 & \frac{51}{50}\end{matrix}\right)$
10

The integral of $\frac{7x^2-9x+2}{\left(x^2+1\right)\left(x-3\right)^2}$ in decomposed fraction equals

$\int\left(\frac{-\frac{51}{50}x+\frac{7}{50}}{x^2+1}+\frac{19}{5\left(x-3\right)^2}+\frac{51}{50\left(x-3\right)}\right)dx$
11

Expand the integral $\int\left(\frac{-\frac{51}{50}x+\frac{7}{50}}{x^2+1}+\frac{19}{5\left(x-3\right)^2}+\frac{51}{50\left(x-3\right)}\right)dx$ into $3$ integrals using the sum rule for integrals, to then solve each integral separately

$\int\frac{-\frac{51}{50}x+\frac{7}{50}}{x^2+1}dx+\int\frac{19}{5\left(x-3\right)^2}dx+\int\frac{51}{50\left(x-3\right)}dx$
12

We can solve the integral $\int\frac{19}{5\left(x-3\right)^2}dx$ 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 $x-3$ it's a good candidate for substitution. Let's define a variable $u$ and assign it to the choosen part

$u=x-3$
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

$du=dx$
14

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

$\int\frac{-\frac{51}{50}x+\frac{7}{50}}{x^2+1}dx+\frac{1}{5}\int\frac{19}{u^2}du+\int\frac{51}{50\left(x-3\right)}dx$
15

The integral $\int\frac{-\frac{51}{50}x+\frac{7}{50}}{x^2+1}dx$ results in: $-\frac{51}{50}\int\frac{x}{x^2+1}dx+\frac{7}{50}\arctan\left(x\right)$

$-\frac{51}{50}\int\frac{x}{x^2+1}dx+\frac{7}{50}\arctan\left(x\right)$
16

The integral $\frac{1}{5}\int\frac{19}{u^2}du$ results in: $\frac{-19}{5\left(x-3\right)}$

$\frac{-19}{5\left(x-3\right)}$
17

Gather the results of all integrals

$\frac{7}{50}\arctan\left(x\right)-\frac{51}{50}\int\frac{x}{x^2+1}dx+\frac{-19}{5\left(x-3\right)}+\int\frac{51}{50\left(x-3\right)}dx$
18

We can solve the integral $-\frac{51}{50}\int\frac{x}{x^2+1}dx$ by applying integration method of trigonometric substitution using the substitution

$x=\tan\left(\theta \right)$
19

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

$dx=\sec\left(\theta \right)^2d\theta$
20

Substituting in the original integral, we get

$\frac{7}{50}\arctan\left(x\right)-\frac{51}{50}\int\frac{\tan\left(\theta \right)\sec\left(\theta \right)^2}{\tan\left(\theta \right)^2+1}d\theta+\frac{-19}{5\left(x-3\right)}+\int\frac{51}{50\left(x-3\right)}dx$
21

Applying the trigonometric identity: $1+\tan\left(\theta \right)^2 = \sec\left(\theta \right)^2$

$\frac{7}{50}\arctan\left(x\right)-\frac{51}{50}\int\frac{\tan\left(\theta \right)\sec\left(\theta \right)^2}{\sec\left(\theta \right)^2}d\theta+\frac{-19}{5\left(x-3\right)}+\int\frac{51}{50\left(x-3\right)}dx$
Why is tan(x)^2+1 = sec(x)^2 ?
22

Simplify the fraction $\frac{\tan\left(\theta \right)\sec\left(\theta \right)^2}{\sec\left(\theta \right)^2}$ by $\sec\left(\theta \right)^2$

$\frac{7}{50}\arctan\left(x\right)-\frac{51}{50}\int\tan\left(\theta \right)d\theta+\frac{-19}{5\left(x-3\right)}+\int\frac{51}{50\left(x-3\right)}dx$
23

We can solve the integral $\int\frac{51}{50\left(x-3\right)}dx$ 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 $x-3$ it's a good candidate for substitution. Let's define a variable $u$ and assign it to the choosen part

$u=x-3$
24

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

$du=dx$
25

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

$\frac{7}{50}\arctan\left(x\right)-\frac{51}{50}\int\tan\left(\theta \right)d\theta+\frac{-19}{5\left(x-3\right)}+\frac{1}{50}\int\frac{51}{u}du$
26

The integral $-\frac{51}{50}\int\tan\left(\theta \right)d\theta$ results in: $-\frac{51}{100}\ln\left(x^2+1\right)$

$-\frac{51}{100}\ln\left(x^2+1\right)$
27

The integral $\frac{1}{50}\int\frac{51}{u}du$ results in: $\frac{51}{50}\ln\left(x-3\right)$

$\frac{51}{50}\ln\left(x-3\right)$
28

Gather the results of all integrals

$\frac{7}{50}\arctan\left(x\right)-\frac{51}{100}\ln\left(x^2+1\right)+\frac{-19}{5\left(x-3\right)}+\frac{51}{50}\ln\left(x-3\right)$
29

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

$\frac{7}{50}\arctan\left(x\right)-\frac{51}{100}\ln\left(x^2+1\right)+\frac{-19}{5\left(x-3\right)}+\frac{51}{50}\ln\left(x-3\right)+C_0$

Final answer to the problem

$\frac{7}{50}\arctan\left(x\right)-\frac{51}{100}\ln\left(x^2+1\right)+\frac{-19}{5\left(x-3\right)}+\frac{51}{50}\ln\left(x-3\right)+C_0$

Explore different ways to solve this problem

Give us your feedback!

Function Plot

Plotting: $\frac{7}{50}\arctan\left(x\right)-\frac{51}{100}\ln\left(x^2+1\right)+\frac{-19}{5\left(x-3\right)}+\frac{51}{50}\ln\left(x-3\right)+C_0$

SnapXam A2
Answer Assistant

beta
Got a different answer? Verify it!

Go!
1
2
3
4
5
6
7
8
9
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

6. See formulas

Your Math & Physics Tutor. Powered by AI

Available 24/7, 365.

Unlimited step-by-step math solutions. No ads.

Includes multiple solving methods.

Support for more than 100 math topics.

Premium access on our iOS and Android apps as well.

20% discount on online tutoring.

Choose your subscription plan:
Have a promo code?
Pay $39.97 USD securely with your payment method.
Please hold while your payment is being processed.
Create an Account