Lines and Slope || Chameleon Home || Ask Dr. Math
An axis is a line that we use to find points and other lines. If we want to talk about more than one axis, we say "axes."
In the plane, we use two axes called the x-axis and the y-axis. Here is a picture:
The x-axis has equation y = 0, and the y-axis has equation x = 0.
When you camouflage yourself, you change to match your surroundings. For example, you might cover your face with mud and put leaves in your hair so that you could hide in a forest. Soldiers often wear clothing that camouflages them.
A chameleon is a type of lizard. Chameleons have long, sticky tongues for catching bugs. They can change color to warm up or cool off, and to camouflage themselves. Chameleons also change color when they are angry or scared.
Chameleons can move one eye without moving the other. This makes it easy for them to keep track of their surroundings.
An equation shows that two things are equal. For example, the equation x = 8 tells you that x and 8 have the same value.
A horizontal line is completely flat. This line is horizontal:
A line's x-intercept is the place that it crosses the x-axis, and its
When two lines cross each other, we say that they intersect. This is the same idea as the intersection of two roads.
In geometry, lines are always straight. Lines are one-dimensional, and they go on forever in both directions. Here is a picture of a line:
(The arrows are supposed to show that the line continues forever.)
Part of a line is called a line segment. Here is a picture:
The dots stand for the points at each end of the segment. If the points at each end aren't included, we use circles instead of dots:
The origin is the point (0, 0).
Two lines are parallel if they never meet. Here is a picture of two parallel lines:
Two lines are perpendicular if their intersection has a 90° angle, like the corner of a square. These two lines are perpendicular:
A point is one location in space. Points are zero-dimensional.
Slope is a number that shows how steeply a line slants. We often use the letter m to stand for a line's slope.
In math, we call something undefined when we can't think of a description that makes sense. For example, 6/2 is a number that you can multiply by two to get six:
2*3 = 6.
This means 6/0 ought to be a number that you can multiply by zero to get six. But zero multiplied by anything is zero, not six. We can't pick a good number for 6/0, so we say that it is undefined. (For more, see Dividing by Zero from the Ask Dr. Math FAQ.)
Vertical lines point straight up and down. This line is vertical:
A vertical line always has the same x-coordinate, which we'll call a. This means that the line's equation is x = a.
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to Ursula Whitcher
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