Question

x в кубе -8x = 7 найдите x

Answer 1

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Answer 2

${x}^{3} - 8x = 7 \\ {x}^{3} - 8x - 7 = 0 \\ (x + 1)( {x}^{2} - x - 7) = 0 \\ - - - - - \\ x + 1 = 0 \\ x1 = - 1 \\ - - - - - \\ {x}^{2} - x - 7 = 0 \\ d = 1 - 4 \times ( - 7) = 1 + 28 = 29 \\ x2 = \frac{1 + \sqrt{29} }{2} \\ x3 = \frac{1 - \sqrt{29} }{2}$