Question

Знайти корені x² +4x -21 =0

Answer 1

Ответ:

x1=-7

x2=3

Объяснение:

${x}^{2} + 4x - 21 = 0 \\ d = {b}^{2} - 4ac \\ d = {4}^{2} - 4 \times 1 \times (- 21) = 16 + 84 = 100 \: \: \sqrt{d} > 0 \\ d = \sqrt{100} = 10 \\ x1 = \frac{ - b - \sqrt{d} }{2a} = \frac{ - 4 - 10}{2} = \frac{ - 14}{2} = - 7 \\ x2 = \frac{ - b + \sqrt{d} }{2a} = \frac{ - 4 + 10}{2} = \frac{6}{2} = 3$