Which substituation would I need to use for this intergral;
[y.du/(y^2 + (x - u)^2)]
The integrand looks like [tex]1/(1+x^2)[/tex] which has antiderivative arctan(x). Try to make substitutions to match that expression.
Got it, take the y out the intergral, make b=x-u then db=-du sub in and use the arctan intergral, getting -tan^-1((x-u)/y)
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