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In algebra, you were introduced to the coordinate system, plotting ordered pairs, and graphing
lines. These tools are used in geometry as well. Algebra and geometry are used hand-in-hand to
solve many real-world math problems.
Points, lines, line segments, rays, and angles, as well as other geometric shapes, can be
graphed on the coordinate plane.
In above figure, A is a point, BC is a line,
DE is a line segment, FG is a ray and JKL
is an angle.
In geometry, lines often occur in pairs. We can define four different types of line pairs: lines that
intersect, lines that are perpendicular, lines that are parallel, and lines that are skew.
If we look at the box, line segments formed by the edges of the box and find two line segments that
intersect. For example, line segment DH and line segment HG
share one point in common, point
H, so they are intersecting line segments.
Perpendicular lines intersect at right angles. You'll learn more about right angles in the next
lesson. The x and y axes on the coordinate plane are a good example of perpendicular lines. This
box has many perpendicular line segments. For example, the intersecting line segments
BF and
EF are perpendicular.
Parallel lines never touch, and always lie in the same plane. For example, line segments BF and
DH are parallel.
Like parallel lines, skew lines never touch, but unlike parallel lines, skew lines are not in the same
plane. Look at edge CG on the right front side of the box, going up and down, and edge AB at the
back, going left to right. These segments are an example of skew lines.
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