Algebra: Chapter 7, Lesson 1, page 304.
Coordinates
Coordinates are defined as `(x, y)` where the x-axis runs left to right and the y-axis runs up and down. The origin is where the points `(0, 0)` exists. A fancy word for the x-axis is the abscissa and the y-axis is the ordinate. There are 4 quadrants:
- I – both `x` and `y` axis have positive value (upper right)
- II– `x` axis is negative and `y` axis is positive (upper left)
- III – both `x` and `y` axis have negative values (lower left)
- IV – `x` axis has positive value, while the `y` axis has negative value (lower right)
By substituting a coordinate pair `(x, y)` into a linear equation, we can determine if the ordered pair is a solution to the linear equation. Just substitute for `x` the value of the first of the ordered pair, and substitute for `y`, the second value of the ordered pair. If the evauation is true, then the ordered pair fits on the line.
Here is a good links from purplemath.com, the first about graphing in general for lesson 7-1.