Let x>0x>0x>0, y>0y>0y>0, a>0 a>0\,a>0 and a≠1a\ne1a=1.
Starting from the definition of a logarithm, prove that loga(xy)=logax−logay\log_a\left(\dfrac{x}{y}\right)=\log_a x-\log_a yloga(yx)=logax−logay.