To show that an equation is not an identity, we must find at least value(s) of the variable that result(s) in both sides being defined but

I believe the answers are one and unequal, 
The major difference between an equation and an identity is that the identity is always true, whereas an equation is only conditionally true, which means it is true for only specific values.
For example if we insert x=5 in  (x-2)^2 = 1, we get 9 =1; which is not true, thus this is an equation, and if we consider an equation like; (x-2)^2=x^2-4x+4, all the values will satisfy the equation and therefore it is an identity.