The lines px+qy+r=0,qx+ry+p=0andrx+py+q=0 are concurrent then
∣∣ ∣∣pqrqrprpq∣∣ ∣∣=0
p(rq−p2)−q(q2−rp)+r(qp−r2)=0
3pqr−p3−q3−r3=0
p3+q3+r3=3pqr
p3+q3+r3−3pqr=0
(p+q+r)(p2+q2+r2−pa−qr−pr)=0
⇒p+q+r=0 or
p2+q2+r2−pq−qr−pr=0
Three lines px+qy+r=0,qx+ry+p=0 and rx+py+q=0 are concurrent, if
p3+ q3 + r3 – 3pqr = ?