>(btw, do i need to register or anything?

No, you do not.

>x=(a*c)/(a^2 b^2), y=(b*c)/(a^2 b^2)

This is correct.

>4c(ax by) 2abxy-a^2*y^2-b^2*x^2
>---------------------------------------------------------- =
>0
> a^2 b^2

This is correct, except you may remove the positive denominator.

>SUB getval (x)
> '
> ' formula used
> ' b -sqrt(b^2-4ac)
> '

But what are a, b, c, and x?

Assume you try solving Ay2 - By + C = 0. Then the formula will be

y1,2 = (B ± sqrt(B2 - 4AC))/2A.

In your case,

A = a2,
B = 4bc + 2abx,
C = b2x2 - 4acx,

where a, b, c, and x are as they are used in your problem description.