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If x + 1/x = 9 find the value of x4 + 1/ x4. |
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Answer» We know that x + 1/x = 9 So when squaring both sides, we get (x + 1/x)2 = (9)2 x2 + 2 × x × 1/x + (1/x)2 = 81 x2 + 2 + 1/x2 = 81 x2 + 1/x2 = 81 – 2 x2 + 1/x2 = 79 Now again when we square on both sides we get, (x2 + 1/x2)2 = (79)2 x4 + 2 × x2 × 1/x2 + (1/x2)2 = 6241 x4 + 2 + 1/x4 = 6241 x4 + 1/x4 = 6241- 2 x4 + 1/x4 = 6239 ∴ x4 – 1/x4 = 6239 |
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