Finding the slope of a line that is perpendicular

Finding the slope of a line that is perpendicular

by Dawn Allen

​What does perpendicular mean?

​This sign shows an example

​of perpendicular lines. The

​two lines create a 90 degree

​angle or a right angle.

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​This is the symbol for a right angle

​This tells me that two

​lines are perpendicular.

​What does slope have to do with it?

​When two lines are perpendicular, there is a relationship between the two slopes.

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There are what mathematicians call

opposite reciprocals.

​Fancy math words that are easy to translate.

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Flip and Switch

​ AND

​Flip and Switch for real

​First we flip, then we switch.

Multiple Choice

What is the slope of a line perpendicular to a line with slope ^-6/₅ ?

• ^-6/₅
• ^-5/6
• ⁵/₆
• ^-4/₃

Multiple Choice

What is the slope of a line perpendicular to -10/3

• -10/3

• 10/3

• 3/10

• -3/10

Multiple Choice

What is the slope of a line perpendicular to 5?

• 5

• 1/5

• -1/5

• -5

Multiple Choice

What slope is perpendicular to:  
m = 5/8

• -5/8
• 5/8
• -8/5
• 8/5

Multiple Choice

What slope is perpendicular to:  
m = 3

• -3
• -1/3
• 1/3
• 3

Multiple Choice

A line is perpendicular to    y = 2x - 7.
What is the slope of this line? 

• -2
• 1/2
• -1/2
• 2