3x^2-25x-28=0, D=961, x1=-1, x2=9 1/3, 3x^2-25x-28=3(x+1)(x-9 1/3)=(x+1)(x-28) 2x^2+13x-7=0, D=225, x1=-7, x2=1/2, 2x^2+13x-7=2(x+7)(x-1/2)=(x+7)(x-1)