Method 1: Take two points to establish a straight line, calculate the analytical formula of the straight line, and substitute the coordinates of the third point to see if the analytical formula (straight line and equation) is satisfied.

Method 2: Let three points be A, B and C, and prove by vector: λAB=AC (where λ is a non-zero real number).

Method 3: Calculate AB slope and AC slope by the point difference method, which is equal to the three-point * * * line.

Method 4: Using Menelaus Theorem.

Method 5: Using the axiom in geometry that "if two non-overlapping planes have a common point, they have only one common straight line passing through the point", we can know that if three points belong to two intersecting planes, they are a straight line.

Method 6: Apply the axiom that there is only one straight line parallel (perpendicular) to the known straight line at a point outside the straight line. Actually, it's the same method.