I am maximizing and minimizing the optimum. Once I had this quadratic function, f(x)=-[x^2-4x+4-4-2] the book says I factor it into vertex form. Giving me two equations in vertex form, f(x)=-(x-2)^2-6 and f(x)=-(x-2)^2+6. Any help understanding the factoring of that quadratic function?