\n<\/p><\/div>"}. Substitute the x values of the equation to find the values of y. An equation that forms a straight line on a graph. What do you mean by "...side to side"? Whereas positive-value slopes travel upward, negative-value slopes travel downward. Everything you need to prepare for an important exam!K-12 tests, GED math test, basic math tests, geometry tests, algebra tests. This image may not be used by other entities without the express written consent of wikiHow, Inc.