http://www.ck12.org Chapter 1. Basics of Geometry
1.2 Distance Between Two Points
Here you’ll learn how to measure using a ruler, how to add segments, and how to place line segments on a coordinate
grid.
The average adult human body can be measured in “heads.” For example, the average human is 7-8 heads tall.
When doing this, keep in mind that each person uses their own head to measure their own body. Other interesting
measurements are in the picture below.
What if you wanted to determine other measurements like the length from the wrist to the elbow or the length from
the top of the neck to the hip? After completing this Concept, you will know how to accurately measure using many
different units of measurement.
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Click image to the left for more content.CK-12 Foundation: Chapter1DistanceBetweenTwoPointsA
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Click image to the left for more content.James Sousa:Ruler PostulateandSegmentAddition Postulate
Guidance
Distanceis the length between two points. Tomeasureis to determine how far apart two geometric objects are. Inch-
rulers are usually divided up by^18 -in. (or 0.125 in) segments. Centimeter rulers are divided up by 101 -centimenter (or
0.1 cm) segments.
The two rulers above are NOT DRAWN TO SCALE.Anytime you see this statement, it means that the measured
length is not actually the distance apart that it is labeled. You should never assume that objects are drawn to scale.
Always rely on the measurements or markings given in a diagram.
TheRuler Postulatestates that the distance between two points will be the absolute value of the difference between
the numbers shown on the ruler. The ruler postulate implies that you do not need to start measuring at “0”, as long
as you subtract the first number from the second. “Absolute value” is used becausedistance is always positive.
Before we introduce the next postulate, we need to address what the word “between” means in geometry.