Perpendicular Lines and Slope

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Perpendicular Lines and Slope
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Perpendicular Lines

• A line is perpendicular to another if it meets or
  crosses at right angles (90). For instance, a
  horizontal and a vertical line are perpendicular
  lines.

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Slopes of Perpendicular Lines

• Complete the following assuming Line A and Line B
  are perpendicular.
• Make Line A have a slope of .
• What is the slope of Line B (the line
  perpendicular to Line A)?

-3
2
3
2
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Slopes of Perpendicular Lines

• Two lines are perpendicular if their slopes are
  opposite reciprocals of each other. In other
  words, if the slope of a line is then the
  perpendicular line has a slope of .
• Example What is the slope of a line
  perpendicular to each equation below.

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Note The y-intercepts Normally are Not the Same
 
 
 
 

• 99.9 of the time, if two lines are parallel or
  perpendicular, they will NOT have the same
  y-intercept. (In fact, only RARELY do
  perpendicular lines share a y-intercept. If lines
  with the same slope have the same y-intercept,
  the lines coincide and are not parallel.)

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Example

• Algebraically find the equation of the line that
  goes through the point (2,3) and is perpendicular
  to y -4x 2.

This y-intercept does not matter.
Find the y-intercept.
Use Slope-Intercept Form
The slope is ¼
A point on the graph is x2 and y-3
The equation now has one distinct variable.
Solve it.
Substitute back into Slope-Intercept Form