Parallel and perpendicular are relative terms. In other words, something can only be parallel or perpendicular to something else. To say that a horizontal line is perpendicular, for example, doesn't make any sense. Perpendicular to what? To say that a horizontal line is perpendicular to a vertical line, however, does make sense.

So let's assume you forgot to include the second equation in your question. If you want to find out if two lines are parallel or perpendicular, rewrite each of them in slope-intercept form (y=mx+b). In order for the two lines to be parallel, the slopes, m, have to be the same. In order to be perpendicular to each other, the slopes must be negative reciprocals of each other.

The equation in your question is



To put it in slope-intercept form, you need to get y all by itself, so you simply divide both sides by -5.



Now you can see that the slope is -2/5. So any line with the same slope will be parallel to it. Any line with a slope of 5/2 (the negative reciprocal) will be perpendicular to it.