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    Question

    If x + y + z = 9 and (x2┬а+ y2┬а+

    z2) = 21, then find the value of (xy + yz + zx)
    A 44 Correct Answer Incorrect Answer
    B 30 Correct Answer Incorrect Answer
    C 24 Correct Answer Incorrect Answer
    D 32 Correct Answer Incorrect Answer

    Solution

    (x + y + z)2┬а= x2┬а+ y2┬а+ z2┬а+ 2 ├Ч (xy + yz + xz) Or, 92┬а= 21 + 2 ├Ч (xy + yz + xz) Or, 2 ├Ч (xy + yz + xz) = 81 тАУ 21 Or, (xy + yz + xz) = 60 ├╖ 2 = 30

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