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    Question

    If x + y + z = 10 and x² + y² + z² = 36, then what is

    the value of x y + y z + z x?
    A 32 Correct Answer Incorrect Answer
    B 40 Correct Answer Incorrect Answer
    C 42 Correct Answer Incorrect Answer
    D 24 Correct Answer Incorrect Answer

    Solution

    (x + y + z) ² = x²+y²+z²+2(x y+y z+z x) (10) ²= 36 + 2(x y+y z+z x) 2(x y+y z +z x) = 64 xy+yz+zx = 32

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