V val1 New member Joined Oct 17, 2005 Messages 40 May 14, 2006 #1 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
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
pka Elite Member Joined Jan 29, 2005 Messages 11,978 May 14, 2006 #2 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: \(\displaystyle \L y = \frac{1}{2}\ln (y^2 - 1)\quad \Rightarrow \quad y' = \frac{y}{{y^2 - 1}}\)
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: \(\displaystyle \L y = \frac{1}{2}\ln (y^2 - 1)\quad \Rightarrow \quad y' = \frac{y}{{y^2 - 1}}\)