Page 26 - Algebra

2.7. Parallel and Perpendicular Lines
Parallel lines
Parallel lines are non-intersecting lines that lie in the same plane. Lines that are parallel to each other always have the same slope. When two non-vertical lines have the same slope, then the lines are parallel.
If m1 and m2 are two parallel lines, then
m1 = m2
Perpendicular lines
Two lines that intersect at 90o are called perpendicular lines. The product of the slope of two perpendicular lines is –1.
Let m1 be the slope of line 1 Let m2 be the slope of line 2 For perpendicular lines m1m2 = –1
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Algebra I & II