Quadratic says there are two answers. Problem tells you that both roots are "5"
{{{y = (x-5)(x-5)}}}
{{{y = (x-5)^2}}}
{{{y = x^2 - 10x + 25}}}

Graph is here --> http://www06.wolframalpha.com/input/?i=y+%3D+(x-5)(x-5)