I dont get how to define a coplanar and collinear?  

⚑ Flag

coplanar is like anything that has a line, plane or point.collinear is like point that are on the same line.

coplanar mean all the points lie on a plane or a flat 2-dimensional surface the points can be spread out but have to lie in the plane collinear means are the point lie in one straight lineif points are all collinear then they're also coplanar

Simple.Coplaner: Like the teacher said, Co = together, planer = plane. They are together in the same plane, whatever figure in one planeCollinear: Co = together, linear, sounds like line, right? Three points on the same line. That's collinear.Hope it helped.Have funCheers.