How does one integrate u√(1+u^2) du?

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SUMMARY

The integral of u√(1+u²) du can be solved using the method of substitution. The correct answer is (1/3)(1 + u²)^(3/2). To derive this, one should let v = 1 + u², which leads to dv = 2u du, allowing for a straightforward substitution. This method emphasizes the importance of recognizing when to apply substitution multiple times for complex integrals.

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Homework Statement


How does one integrate u√(1+u^2) du?

Homework Equations


Forget what u is being substituted for. It doesn't really matter right now. I just need to integrate what is typed above.

The Attempt at a Solution


I am completely lost and not sure what to do.
 
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Rosebud said:

Homework Statement


How does one integrate u√(1+u^2) du?

Homework Equations


Forget what u is being substituted for. It doesn't really matter right now. I just need to integrate what is typed above.

The Attempt at a Solution


I am completely lost and not sure what to do.
What's the derivative of 1+u2 ?
 
SammyS said:
What's the derivative of 1+u2 ?
The derivative of 1+u^2 with respect to u is 2u du.

I know the answer is (1/3)(1 + u^2)^(3/2) but I don't know how to find it.
 
Rosebud said:
The derivative of 1+u^2 with respect to u is 2u du.

I know the answer is (1/3)(1 + u^2)^(3/2) but I don't know how to find it.
Do you know the method of substitution ?
 
SammyS said:
Do you know the method of substitution ?
No.
 
Rosebud said:
The derivative of 1+u^2 with respect to u is 2u du.

I know the answer is (1/3)(1 + u^2)^(3/2) but I don't know how to find it.
That should have been a BIG hint.

Take the derivative of (1/3)(1 + u^2)^(3/2) . Then work backwards.
 
SammyS said:
That should have been a BIG hint.

Take the derivative of (1/3)(1 + u^2)^(3/2) . Then work backwards.
Thanks for the tip. I did that but I still fail to see the connection. Can you, or someone else, give me the next step?
 
Let v= 1+u^2
so dv=2u du

how do you replace du and (1+u^2)
 
DeldotB said:
Let v= 1+u^2
so dv=2u du

Notice you have a u in the numerator. So what can you do to replace the numerator with dv ?
Numerator? There is no fraction here unless you you consider 1 as the denominator.
 
  • #10
Rosebud said:
Numerator? There is no fraction here unless you you consider 1 as the denominator.
ahh, thought I saw a / in front of the root.
fixed it. That partial square root symbol gets me
 
  • #11
Rosebud said:
The derivative of 1+u^2 with respect to u is 2u du.

I know the answer is (1/3)(1 + u^2)^(3/2) but I don't know how to find it.
That helped immensely. Thank you so much. I forgot that I could use substitution more than once.
 
  • #12
SammyS said:
Do you know the method of substitution ?
Rosebud said:
No.
So, you do know substitution.
 
  • #13
Rosebud said:
That helped immensely. Thank you so much. I forgot that I could use substitution more than once.

Of course a substitution in a substitution is still one substitution overall so you can substitute twice all at once, but maybe it is better to go by stages at first. :oldsmile:
 
  • #14
SammyS said:
So, you do know substitution.
Yes, I know substitution. You asked me if I knew the method of substitution, which I understood as, you asking if I knew which method of substitution that I should use.
 
  • #15
1 + [sinh^2(x)] = [cosh^2(x)]
 

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