Multiply numerator and denominator by sin(x) * cos(x), getting: 
((sin(x) * cos(x)) - cos^2(x) / (((sin^2(x)) - (sin(x) * cos(x))) = 
(cos(x) * (sin(x) - cos(x))) 
------------------------------------ 
(sin(x) * (sin(x) - cos(x))) 
and after you cancel the two identical terms (sin(x) - cos(x)), you have: 
cos(x) 
----------- = cot(x) <--------------- Answer 
sin(x)