20: abc, abd, abe, abf, acd, ace, acf, ade, adf, aef, bcd, bce, bcf, bde, bdf, bef, cde, cdf, cef, def.
a straight line ..
Quadrilaterals and triangles.
A polygon is a plane figure bounded by a finite number of straight lines. To enclose an area then a minimum of three straight lines are required. All triangles, not just isosceles triangles, are polygons.
I believe that is the definition of a straight line.
A plane is a straight line. An angls is formed by 2 intersecting lines.
84
The least number of obtuse triangles, if all possible triangles are drawn for n points in a plane, is zero. If all the n points lie in a straight line, no triangles are possible and so no obtuse triangles are able to be drawn; thus for any number n, there is a possibility that no obtuse triangles can be drawn, so the least possible number of obtuse triangles drawn is zero.
a straight line ..
Quadrilaterals and triangles.
They are closed plane figures bounded by straight lines.
I believe that is the definition of a straight line.
A polygon is a plane figure bounded by a finite number of straight lines. To enclose an area then a minimum of three straight lines are required. All triangles, not just isosceles triangles, are polygons.
If it is a straight line it must be in the same plane. Otherwise not necessarily.
Two points in a plane.
They are made of straight lines, all in one plane, such that pairs of them meet at vertices.
A plane is a straight line. An angls is formed by 2 intersecting lines.
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 !?!