SOLUTION: Solve this indefinite integral ∫ 6dx/〖x(3x+1)〗by using the following formula: ∫ dx/(x(mx+b))=1/b In |x/(mx+b)|

Algebra ->  Exponential-and-logarithmic-functions -> SOLUTION: Solve this indefinite integral ∫ 6dx/〖x(3x+1)〗by using the following formula: ∫ dx/(x(mx+b))=1/b In |x/(mx+b)|       Log On


   



Question 1157386: Solve this indefinite integral ∫ 6dx/〖x(3x+1)〗by using the following formula:
∫ dx/(x(mx+b))=1/b In |x/(mx+b)|

Found 3 solutions by KMST, ikleyn, math_tutor2020:
Answer by KMST(5434) About Me  (Show Source):
You can put this solution on YOUR website!
The formula is
int%28dx%2F%28x%28mx%2Bb%29%29%29%22=%22%281%2Fb%29%22ln%22abs%28x%2F%28mx%2Bb%29%29 , where ln%28x%29 is the function natural logarithm.
The indefinite integral to solve is
int%286dx%2F%28x%283x%2B1%29%29%29which is equal to 6int%28dx%2F%28x%283x%2B1%29%29%29 ,
as anyone starting to learn about indefinite integrals in calculus class would know.
We notice that int%28dx%2F%28x%28mx%2Bb%29%29%29 turns into int%28dx%2F%28x%283x%2B1%29%29%29 for system%28m=3%2Cb=1%29 .
So, applying the given formula, we confidently write
int%286dx%2F%28x%283x%2B1%29%29%29%22=%226int%28dx%2F%28x%283x%2B1%29%29%29%22=%226%281%2F1%29%22ln%22abs%28x%2F%283x%2B1%29%29%22=%226%22ln%22abs%28x%2F%283x%2B1%29%29

IMPORTANT NOTE:
When we write dx%2F%28x%28mx%2Bb%29%29 on paper, it does mean dx/[x(mx+b)],
and we do not need the square bracket around x%28mx%2Bb%29 ,
because that horizontal line between dx and x%28mx%2Bb%29 comes with invisible brackets around the expressions above and under it.
That horizontal line is a grouping symbol, just like the square root symbol.
However, when we have to type expressions in one line we need the extra brackets.
If you try to key %280.723-0.002%29%2F%280.745-0.001%29 into a calculator,
you must type as (0.723-0.002)/(0.745-0.001).
If you skip the brackets, almost all calculators will calculate
0.723 %22-%22 0.002%2F0.745 %22-%22 0.001 ,
because modern calculators use algebraic language, and know the conventions about order of operations.

Answer by ikleyn(54018) About Me  (Show Source):
You can put this solution on YOUR website!
.
Solve this indefinite integral ∫ 6dx/〖x(3x+1)〗by using the following formula:
∫ dx/(x(mx+b))=1/b In |x/(mx+b)|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


The formula in the problem is incomplete.

The correct formula and the correct answer for indefinite integral is

int%286dx%2F%28x%283x%2B1%29%29%29%22=%226%22ln%22abs%28x%2F%283x%2B1%29%29 + C,

which sounds "plus a constant".


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About this "plus a constant", there is a famous mathematical joke /(an anecdote story).
See it and read it under this link

https://www.dsprelated.com/thread/14755/one-of-my-favorite-mathematics-jokes



Answer by math_tutor2020(3847) About Me  (Show Source):
You can put this solution on YOUR website!

Don't forget the "plus C". This is a common mistake I've seen many calculus students do.
Also, you wrote "in" instead of "Ln" for the formula you posted.
Ln represents the natural log.
It's unfortunate that the uppercase version of "i" looks a lot like the lowercase version of "L".




Plug in m = 3 and b = 1





Multiply both sides by 6








Note the 6C becomes C since both represent a constant.
In other words, 6*constant = some other constant.