Why is the Constant 1/2 Used in Evaluating Integrals and Differentials?

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Homework Help Overview

The discussion revolves around understanding the appearance of the constant 1/2 in the evaluation of the integral \(\int\frac{x}{x^2+1}dx\), specifically questioning its derivation and significance in the context of calculus.

Discussion Character

  • Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the relationship between the integral and its derivative, with some suggesting that taking the derivative of the result could clarify the presence of the constant. Others mention using substitution as a method to evaluate the integral.

Discussion Status

The conversation includes attempts to guide the original poster towards understanding through hints about differentiation and substitution. However, there is a noted frustration from the original poster regarding the clarity of the responses, indicating that the discussion is ongoing without a clear resolution.

Contextual Notes

There is a suggestion that the original poster may not be fully prepared to apply the substitution method effectively, and a reminder about the importance of the chain rule in calculus is mentioned. The discussion reflects varying levels of understanding among participants.

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Can someone explain to me why \int\frac{x}{x^2+1} = \frac{1}{2}ln(x^2+1) WHERE DOES THE ONE HALF COME FROM ?
 
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Take the derivative of the right hand side and find out for yourself. (Hint: Chain rule.)
 


(ln(u))' = \frac{u'}{u}
 


ok none of these responses helped me at all.
 


Did you take the derivative of the right hand side?
 


You can also evaluate the LHS i.e. the integral

Hint #1 - it's a u-subst.

Hint #2 - let u = x^2 + 1
 


I'm sorry but the OP has no business trying a u-sub if he doesn't follow the first hint. The idea that you can take the derivative to verify the correctness of an integral is fundamental. Remembering to apply the chain rule answers the question. I mean sure, he could apply a technique that really follows from these basic principles but then it would be hard to tell if he actually knew why.
 

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