Question 20887
If you are asking how to determine if an equation is a function or not, I think I can give you an example. You didn't give any numbers so I will.  
first start with the definition of a function:
a function "F" from set A to set B is a rule of correspondence that assigns to each element in A exactly one element in B.  In other words there can be only one answer for it to be a function. for example:

-x^2 + y = 3
y= x^2 + 3

this equation
can only give
one answer, it is a function

However, 
-x + y^2 = 3
y^2= x + 3
y =  the square root of x+3 and the neg. of the square root of x+3

this equation has more than one answer and therefore cannot be a function.

Hope this helps you with your problem.....