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Using a number line, let's learn how we measure segments.
Before learning any new concept (mathematical or otherwise), it's important we learn and use a common language and label concepts consistently.
In this example of measuring a line segment, the numbers span across the positive and negative. Remember, line segments and points are the foundations of geometry, so this is an important concept.
Let's take line segments a little further. How do we know if line segments are congruent? Let's watch this example of counting points to see if they have the exact same length.