The last topic that we have to discuss in this section is that of parallel & perpendicular lines. Following is a sketch of parallel and perpendicular lines.
Suppose that the slope of Line 1 is m1 and the slope of Line 2 is m2. We can relate the slopes of parallel lines & we can relate slopes of perpendicular lines as.
parallel : m1 = m2
perpendicular : m1m2 = -1 or m2= -1/m1
Note down that for perpendicular lines there are two forms of the equation. The second is the morecommon & in this case usually we say that m2 is the negative reciprocal of m1.