Question

X ao quadrado -4x-21=0 calcular as raízes

Answer 1

${x}^{2} - 4x - 21 = 0 \\ \\ {b}^{2} - 4ac \\ { - 4}^{2} - 4 \times 1 \times ( - 21) \\ 16 + 84 = 100 \\ \\ x1 = \frac{ - b + \sqrt{100} }{2a} \\ x1 = \frac{4 + 10}{2} \\ x = 7 \\ \\ x2 = \frac{ - b - \sqrt{100} }{2a} \\ x2 = \frac{4 - 10}{2} \\ x2 = - 3$