Question

If p² + q² + r² = 82 and pq + qr + pr = 18; find p + q + r.

Answer 1

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