25x^2 - 10x + 1 = 0
discriminant = b^2 - 4ac = 100-100 = 0
so, the roots are the same.
(5x-1)(5x-1)
Why does the discriminant determine how many roots? Well, the roots are basically -b/2a +/- the discriminant. So, if the discriminant is zero, both roots are -b/2a
If the discriminant is positive, both roots are the same distance away from -b/2a
If the discriminant is negative, there is no real square root, and we have complex roots.