Exams › SSC CGL (Prelims) › General

If p + q + r = 0 and p^2 + q^2 + r^2 = 40, find the value of pq + qr + rp.

1. -20
2. 5
3. -5
4. -10

Correct answer: -20

Solution

Since p+q+r=0, squaring both sides: 0 = p^2+q^2+r^2 + 2(pq+qr+rp) = 40 + 2(pq+qr+rp). Therefore pq+qr+rp = -20.

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