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    • Question

      If p = 40 - q - r and pq + r(p + q) = 400, then find the

      value of (p² + q² + r²).
      A 810 Correct Answer Incorrect Answer
      B 750 Correct Answer Incorrect Answer
      C 800 Correct Answer Incorrect Answer
      D 768 Correct Answer Incorrect Answer

      Solution

      We have, p = 40 - q - r
      So, p + q + r = 40
      And, pq + r(p + q) = 400
      Or, pq + qr + pr = 400
      Using, (p + q + r)² = p² + q² + r² + 2(pq + qr + pr)
      40² = (p² + q² + r²) + 2 × 400
      1600 = (p² + q² + r²) + 800
      p² + q² + r² = 800

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