[tex]a {x}^{2} + bx + c = a(x - x1)(x - x2) \\ {x}^{2} - 8x + 7 \\ {x}^{2} - 8x + 7 = 0 \\ d = ( - 8 {)}^{2} - 4 \times 1 \times 7 = 64 -28 = 36 \\ x1 = \frac{ - b - \sqrt{d} }{2a} = \frac{8 - 6}{2} = 1 \\ x2 = \frac{ - b + \sqrt{d} }{2a} = \frac{8 + 6}{2} = 7 \\ {x}^{2} - 8x + 7 = 1(x - 1)(x - 7)[/tex]