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    Question

    If ( p = 40 - q - r ) and ( pq + r(q + p) = 720 ), then

    find the value of ( p2 + q2 + r2).
    A 160 Correct Answer Incorrect Answer
    B 180 Correct Answer Incorrect Answer
    C 200 Correct Answer Incorrect Answer
    D 140 Correct Answer Incorrect Answer

    Solution

    We have, ( p = 40 - q - r ) So, ( p + q + r = 40 ) And, ( pq + r(q + p) = 720 ) Or, ( pq + qr + pr = 720 ) Using, ( (p + q + r)2 = p2 + q2 + r2 + 2(pq + qr + pr) ) ((40)2 = (p2 + q2 + r2) + 2 x 720) ((p2 + q2 + r2) = 1,600 - 1,440) ((p2 + q2 + r2) = 160

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