Question

    If (p + q + r) = 4, and (p² + q² + r²) =

    56
    A 20 Correct Answer Incorrect Answer
    B 24 Correct Answer Incorrect Answer
    C 18 Correct Answer Incorrect Answer
    D 16 Correct Answer Incorrect Answer

    Solution

    ATQ,

    We have, (p + q + r) = 4

    Squaring on both sides, we get

    (p + q + r) ² = 4²

    Or, p² + q² + r² + 2(pq + qr + rp) = 16

    Or, 56 + 2(pq + qr + rp) = 16

    Or, 2(pq + qr + rp) = 16 - 56 = -40

    So, (pq + qr + rp) = ( - 40/2) = - 20

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