SATII数学考试快递——Lines and Angles
A line is a collection of points that extends without limit in a straight formation. A line can be named by a single letter, like line l, or it can be named according to two points that it contains, like line AB. The second way of naming a line indicates an important property common to all lines: any two points in space determine a line. For example, given two points, J and K:
a line is determined:
This line is called JK.
Line Segments
A line segment is a section of a line. It is named and determined by its endpoints. Unlike a line, whose length is infinite, a line segment has finite length. Line segment AB is pictured below.
Distance and Midpoint of a Line Segment
The midpoint of a line segment is the point on the segment that is equidistant (the same distance) from each endpoint. Because a midpoint splits a line segment into two equal halves, the midpoint is said to bisect the line segment.
Because a midpoint cuts a line segment in half, knowing the distance between the midpoint and one endpoint of a line segment allows you to calculate the length of the entire line segment. For example, if the distance from one endpoint to the midpoint of a line segment is 5, the length of the whole line segment is 10.
The Math IC test often asks questions that focus on this property of midpoints. The Math IC writers usually make their questions a little trickier though, by including multiple midpoints. Take a look:
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All the midpoints flying around in this question can get quite confusing. Instead of trying to visualize what is being described in your head, draw a sketch of what the question describes.
