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If x4 - 79x2 + 1 = 0, then a value of x + x-1 can be : |
9 5 7 8 |
9 |
If x4 - 79x2 + 1 = 0 If x4 -1 = 79x2 divide by x2 on both sides = If x2 - \(\frac{1}{x^2}\) = n Then, x + \(\frac{1}{x}\) = \(\sqrt {n + 2}\) x2 - \(\frac{1}{x^2}\) = 79 x + \(\frac{1}{x}\) = \(\sqrt {79 + 2}\) = 9 |
