which equation is a function of x

Question

I have choices they are 2x-y^2=9 , x^2-y^2=1,  y=x^2+3x+2, y^2=x^2+4x-5

Answer 1

When y is a function of x, we may write that as:

      y = f(x)

 

Now, you may solve (that is, get y alone on the left side of the equation) for y in these equations, but you must remember that an equation like:

        y² = x

   has two solutions:

        y = + SQRT(x)

        y =  - SQRT(x)

 

So, now, which equation has just a y ?