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    Question

    x = 7 - 4√3 then the value of x³+1/x³ is equal

    to?
    A 2702 Correct Answer Incorrect Answer
    B 2744 Correct Answer Incorrect Answer
    C 5702 Correct Answer Incorrect Answer
    D 3245 Correct Answer Incorrect Answer

    Solution

    x = 7 - 4√3 x + 1/x = 7 - 4√3 + 1/(7-4√3) x + 1/x = 7 - 4√3 + 7 + 4√3 x + 1/x = 14 So x³ + 1/x³ = (14)³ - 3 × 14 = 2744 - 42 = 2702 (x + 1/x = a,  x³ + 1/x³ = a³ - 3a)

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