Where Does the du/2 Come From in the Integral of a Product?

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The discussion clarifies the origin of the du/2 term in the integral of a product involving the substitution u = x^2 + 1. The differential du is derived as du = 2x dx, leading to dx being expressed as du / 2x. When substituting this back into the integral, the x terms cancel, resulting in the du/2 term. The confusion arises from the role of dx in the context of differentiation versus integration.

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Ry122
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In the following problem where does the du/2 come from?
I don't understand why it isn't just du.
http://users.on.net/~rohanlal/partialdif.jpg
 
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They have made the substitution u = x^2+1, hence the corrosponding differential du is given by:

du = 2x dx

Hence, after rearranging:

dx = du / 2x

Sub this back into the integral, and the x's will cancel out, leaving du/2.
 
when differentiating u why does it gain a dx?
dx is usually only present when attempting to find the integral of something, not when stating the derivative of a function.
 

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