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I don't know how to answer this question given in a test recently and I thought someone might be able to help.

Bob adds a number, that is larger than 1, to its reciprocal. His answer is 4. Find Bob's number in the form a (add or subtract) square root of b

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  1. x + 1/x = 4
    x^2 - 4x + 1 = 0
    x = (4±√12)/2 = 2±√3
    2-√3 < 1 so
    x = 2+√3

    check: 1/(2+√3) = 2-√3
    so 2+√3 + 2-√3 = 4

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