if they are parallel they run side by side forever and will never cross. if they are perpendicular they will cross at a 90 degree angle.
You can also tell just by looking at the equations for the lines if they are in the slope-intercept form (y = mx + b, where m is the slope and b is the y-intercept). When two lines are parallel, they have the same slope. When two lines are perpendicular, the slope of one is the negative reciprocal of the slope of other. For example, a line with a slope of 2 is perpendicular to a line with a slope of -½, and a line with a slope of 1 is perpendicular to a line with a slope of -1. (y = 1 and x = 1 are perpendicular because the slope of y = 1 is zero, the slope of x = 1 is infinity, the reciprocal of infinity is zero, and negative zero equals zero.)
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As far as we know, two lines can be perpendicular, or they can be parallel, but they can't be both.
perpendicular cross parallel do not
Please read both answers in case that's what you know because there are two names.a set of lines that are not parallel or perpendicular are called normal lines because no one has thought of a name but one young man in 2000 also came up with the word PARAPENDICEL. {para - pen - dic - eel} he came from a place called abbey mead in Gloucestershire.a set of lines that are not parallel or perpendicular arecalled anomeus lines.
l dnot relly know but it is a
When the lines intersect at a 90º angle