If p, q, r are distinct, then (q-r)x + (r-p) y + (p-q)=0 and (q3−r3)x+(r3−p3)y+(p3−q3)=0 represents the same line if
p+q+r=0
p=q=r
p2+q2+r2=0
p3+q3+r3=0
q3−r3q−r=r3−p3r−p=p3−q3p−q