Question
If (p + q + r) = 4, and (p² + q² + r²) =
56Solution
ATQ,
We have, (p + q + r) = 4
Squaring on both sides, we get
(p + q + r) ² = 4²
Or, p² + q² + r² + 2(pq + qr + rp) = 16
Or, 56 + 2(pq + qr + rp) = 16
Or, 2(pq + qr + rp) = 16 - 56 = -40
So, (pq + qr + rp) = ( - 40/2) = - 20
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