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 m_{1} and the slope of Line 2 is m_{2}. We can relate the slopes of parallel lines & we can relate slopes of perpendicular lines as.
parallel : m_{1} = m_{2}
perpendicular : m_{1}m_{2} = -1 or m_{2}= -1/m_{1}
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 m_{2 }is the negative reciprocal of m_{1}.