Question

Show that the point A(-2,3,5), B(1,2,3) and C(7,0,-1) are collinear .

Answer 1

$AB=\sqrt{(1+2{)}^2+(2+3{)}^2+(3-5{)}^2}=\sqrt{14}$
$BC=\sqrt{56}=2\sqrt{14}$ $CA=\sqrt{126}=3\sqrt{14}$

AB+BC=CA
A, B, C are collinear.