Please can you explain this integration result?

val1

New member
Joined
Oct 17, 2005
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40
Hi
Can someone please explain why \(\displaystyle \L
\int {\frac{1}{{y^2 - 1}}} dy = \frac{1}{2}\ln \frac{{y - 1}}{{y + 1}} + C\)

and not \(\displaystyle \L
\frac{1}{2}\ln (y^2 - 1) + C\)

?

Thanks
 
The antiderivative is done with partial fractions.
\(\displaystyle \L
\frac{1}{{y^2 - 1}} = \frac{1}{{2\left( {y - 1} \right)}} - \frac{1}{{2\left( {y + 1} \right)}}\)

Look at the derivative of your function:
\(\displaystyle \L
y = \frac{1}{2}\ln (y^2 - 1)\quad \Rightarrow \quad y' = \frac{y}{{y^2 - 1}}\)
 
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