Section 1.5 More on Slopes
Parallel and Perpendicular Lines
1.)
Parallel Lines
have the same slope.
(Two lines are parallel if they lie in the same plane and never intersect.)
two distinct vertical lines, both with undefined slopes, are parallel
EX 1:
Write an equation of the line passing through (2, 5) and parallel to the line whose equation is
y = 3x + 1.
Express the equation in pointslope form and slopeintercept form.
2.)
Perpendicular Lines
(Perpendicular lines are two lines who meet at a 90 degree angle.)
 two lines are perpendicular if the product of their slopes is 1
 That is, one line is perpendicular to another if its slope is the negative reciprocal
of the first.
i.e.
negative reciprocal
of
a
=
a
1

 a horizontal line having slope zero is perpendicular to a vertical line having an undefined slope
EX 2:
Find the equation of the line perpendicular to x + 3y – 12 = 0 and that passes through (1, 2).
Slope as Rate of Change
refers to what slope really means when looking at a real relationship between quantities.
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 Fall '08
 Mcbride,V
 Derivative, Slope, average rate

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