The answer depends on the information that you have about the four points and the manner in which that information is presented.
Suppose the 4 points are A, B, C and D and the point that you find is P.
If you have the coordinates of A, B, C and D then
gradient AP = gradient AB (or any other pair) will suffice.
If you have any one of vectors AB (or AC, AD, BC, BD), then
vector AP is parallel to vector AB will suffice.
The answer depends on the number of point. One point - as the question states - cannot be non-collinear. Any two points are always collinear. But three or more points will define a plane. If four points are non-coplanar, they will define four planes (as in a tetrahedron).
Three or more points are collinear if they are all in the same straight line. They are non collinear if at least one of them is not on the same line as the rest. Four or more points are coplanar if they are all in the same plane. They are non coplanar if at least one of them is not on the same plane as the rest.
Four non-collinear points can form exactly one plane. This is because a plane is defined by three non-collinear points, and adding a fourth point that is not in the same line as the other three does not create a new plane; rather, it remains within the same plane defined by the initial three points. Therefore, all four points lie in the same unique plane.
If points m, n, o, and p are arranged such that three of them lie on a straight line, there are two possible scenarios: either three points (e.g., m, n, o) are collinear and the fourth point (p) is not, or all four points are collinear. In the first case, there is one line formed by the three collinear points, and the fourth point can form additional lines with any two of the other three points. Therefore, if only three are collinear, there are multiple lines; if all four are collinear, there is just one line.
not necassarily