If there are three points, there are six possible orders, while "either" implies one of two!
Leaving that aside, convention requires that, in elementary mathematics, the points are given in order - in either direction (ad there are only two possible directions). However, that is not the case with vectors. The order of the points is critical for vectors because, in vector algebra AB = -BA
it is, unless all three points are in the same line (Your "Why" should have be "When")
Its vertices.
Through any three points NOT on the same straight line. If they are all on the same line then that line can act as an axis of rotation for an infinite number of planes containing the three points.
No, given any three points, it is possible for one of the points not to be on the line defined by the other two points. Only two points on a line are needed to identify the exact position of the line. The positions of any three points gives you the exact position of the plane that includes those three points.No, it is not true. If it were true, all triangles would be straight lines !?!
Infinitely many planes contain any two given points- it takes three (non-collinear) points to determine a plane.
it is, unless all three points are in the same line (Your "Why" should have be "When")
3 points
If you're only given two points, and you're told that they both lie on a circle,then there are an infinite number of possible circles, and therefore an infinitenumber of possible centers. In order to pin it down, you need three points.
Its vertices.
They are given three points.
Any three given points can be joined by a common plane, and any two given points can be joined by a common line and an infinite number of common planes.
Yes. In fact, given any three non-collinear points, there is one (and only one) circle that passes through all three points.
One.
There are no planes containing any number of given points. Two points not the same define a line. Three points not in a line define a plane. For four or more points to lie in the same plane, three can be arbitrary but not on the same line, but the fourth (and so on) points must lie in that same plane.
It is impossible to define a parabola with only two points given. An infinite number of parabolic functions will share the two points. Remember that a parabolic function [ax2 + bx1 + cx0] is defined by three coefficients: a, b and c. Two given points only allow you to form two equations with these coefficients. Three equations are generally needed to solve simultaneously for three variables, so three points need to be supplied to pin down your rule/function.
If you are given a plane, you can always find and number of points that are not in that plane but, given anythree points there is always at least one plane that goes through all three.
An arc.