Integration using substitution

In summary, the conversation involved finding the integral of 6/(1+sqrt(7x))dx, using the hint u^2=7x and the substitution method. After obtaining an integrand of (12/7) u/(1 + u) * du, polynomial long division was used to simplify it to 1 + -1/(u + 1). The final answer, 12/7(sqrt(7x)-ln(sqrt(7x)+1)) + C, was found to be correct after adding the constant of integration.
  • #1
Dro
7
0

Homework Statement


Integrate: 6/(1+sqrt(7x))dx

Homework Equations



the hint was that u^2=7x

The Attempt at a Solution


by substituting u, i got the antiderivative of (12/7)(u/(1+u))du so i substituted again and ended up getting 12/7(1+sqrt(7x)-ln(sqrt(7x)+1)) but apparently that's wrong. please help!
 
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  • #2
Assuming that your work is correct in getting to an integrand of (12/7) u/(1 + u) * du, divide u by 1 + u using polynomial long division.
 
  • #3
wouldnt it be easier to substitute another letter like w for 1+u instead? although this did not give me the right number. i don't really get how to divide u by (1+u)
 
  • #5
Actually, I don't see anything wrong with your answer: 12/7(1+sqrt(7x)-ln(sqrt(7x)+1))
except that it is missing the constant of integration.
I get 12/7(sqrt(7x)-ln(sqrt(7x)+1)) + C, which differs from yours by a constant.
 
  • #6
thank you very much! i actually can't put the +C because i have to put it in online but i changed my answer to what you had which differed from mine by the +1 i had and it said I as correct
 

FAQ: Integration using substitution

What is integration using substitution?

Integration using substitution is a technique used in calculus to find the antiderivative of a function. It involves substituting a variable or expression in the integrand with a new variable or expression to simplify the integral.

How do you know when to use substitution for integration?

You should use substitution for integration when the integrand contains a complicated expression or function that can be simplified by substituting a variable or expression. This method is also useful when dealing with trigonometric functions or exponential functions.

What is the process for integration using substitution?

The process for integration using substitution involves choosing a new variable or expression to substitute in the integrand, differentiating it to find its differential, and then replacing the original variable in the integrand with the new variable and its differential. This can help simplify the integral and make it easier to solve.

Are there any tips for choosing the correct substitution?

One tip for choosing the correct substitution is to look for patterns in the integrand. For example, if the integrand contains a polynomial function, it may be helpful to substitute with the highest degree term. Another tip is to try using trigonometric identities for integrals involving trig functions.

Can you use substitution for all integrals?

No, substitution may not work for all integrals. Some integrals may require other integration techniques such as integration by parts or partial fractions. It is important to consider all available methods and choose the most appropriate one for each integral.

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