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Question
If p2 + q2 + r2 = 82 and pq + qr + pr = 18; find p + q + r.
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Solution
(p + q + r)2
= p2 + q2 + r2 + 2pq + 2qr + 2pr
= 82 + 2(18)
= 64 + 36
= 100
⇒ p + q + r
= `sqrt(100)`
= ± 10.
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