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    Question

    If   a 2 + b 2 + c

    >2 = 40 & ab + bc + ca = 12 then  a + b+ c = ?
    A 9 Correct Answer Incorrect Answer
    B 7 Correct Answer Incorrect Answer
    C 8 Correct Answer Incorrect Answer
    D 4 Correct Answer Incorrect Answer

    Solution

    (a+b+c)2 = a2+b2+c2+ 2ab+2bc+2ca So (a+b+c) 2 = 40+2(12) or (a+b+c) 2 = 40 +24 so (a+b+c) 2 = 64 so (a+b+c)  = 8 ` `

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