Multiple Choice Questions on If x 1 radic 5 ndash 2 than x4 16x2 ndash 8x3 ........ for NDA Exam Preparation

Algebra

Mathematics (NDA)

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    If x = 1 /√5 – 2 than x4 + 16x2 – 8x3 = ?

    -5

    Incorrect Answer

    1

    Correct Answer

    –2 √5

    Incorrect Answer

    √5 + 2

    Incorrect Answer
    Explanation:

    x = 1/√5 – 2
    x = √5 + 2
    x – 2 = √5
    x2 – 4x + 4 = 5
    x2 – 4x – 1 = 0 .........(i)
    x2 – 4x + 1 = 2 ..........(ii)
    Multiply eq. (i) by eq. (ii)
    (x2 – 4x – 1) (x2 – 4x + 1) = 0
    (x2 – 4x)2 – 1 = 0
    x4 + 16x2 – 8x3 = 1


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