JEE Advance - Mathematics (1985 - No. 20)
Three lines $$px + qy + r = 0$$, $$qx + ry + p = 0$$ and $$rx + py + q = 0$$ are concurrent if
$$p + q + r = 0$$
$${p^2} + {q^2} + {r^2} = qr + rp + pq$$
$${p^3} + {q^3} + {r^3} = 3pqr$$
none of these.
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