The quadratic formula says that the two solutions to the quadratic equation are given by . I can't see that attachment- just "Purplemath Graphic" so I can't tell what is wrong. Here the equation is . a= 1, b= -2, c= -1 so that becomes

Ah, now I see what your question is. They are using the fact that 8= 4(2) so that because . So the formula reduces to .