Put  over 



Now we use  to make a unit fraction, that is,
one which equals 1.  We have to choose which of these unit 
fractions we need to multiply by.  Our choices are the unit
fractions  and .  We will choose the one with  
on the bottom to multiply by, so that it will cancel 
with the  in the numerator. So we multiply by 



Now we cancel the 's:



We can also cancel the  into the  and get 
 


That leaves



or



Edwin