Basic Postulates (1)
Postulate 5.
If two distinct planes intersect, they intersect at a line.
In the figure above, planes Ƥ and M intersect at
Postulate 6. Ruler Postulate
The points on a line can have a one-to-one correspondence with real numbers such that the distance between two points is the absolute value of the difference of the corresponding numbers.
In the figure above, the length of can be measured using a ruler. Its length, which is denoted by AB, can be calculated using the following formula:
This is read as follows: "the length of line segment AB is equal to the absolute value of the difference of a and b," where a is the coordinate of point A and b is the coordinate of point B.
Note that the length of a segment is calculated by getting the absolute value of the difference of its two coordinates since it should always be positive or nonnegative.
