Question

same gradient = collinear right?

Answer 1

not really; linear means that they all are in a line; same slope means that they are at least parallel lines

Answer 2

if A, B and C form a straight line; from point to point and have the same slope between points; then yes

Answer 3

so by looking at the points can we roughly know isit collinear?

Answer 4

roughly yes; but by sight is never a good solution for precise measurements :)

Answer 5

some points can be quadratic and seem linear just becasue of the part of the curve they are on is to subtile to tell by sight

Answer 6

Do you have an example?