I will put  on the limits to show what variable the
limits are on, namely x, since we will be changing the limits:



Let 
Then 
or 

and 

So we substitute  for  and  for 



And we can take out the negative sign in front of the integral:



But the limits are on x.  We want to change the limits
so that they will be on u rather than x.

To do that we substitute the limits for x in the equation
for u which is 

when ,  and
when , ,
so we change the limits to:



and we use the power formula 
 


Edwin