Understanding Perpendicular Lines and Negative Reciprocal Slopes

Charlie K Self, a math teacher, explains why perpendicular lines have negative reciprocal slopes. He discusses the slopes of vertical and horizontal lines, and how they relate to perpendicularity. The video covers slopes of 1 and -1, and introduces the concept of negative reciprocals. It also explains how proportionality affects the sharpness of slopes, leading to the understanding that perpendicular slopes are negative reciprocals.

What is the main topic of the video?

• Why parallel lines have the same slope

• Why perpendicular lines have negative reciprocal slopes

• How to find the slope of a line

• The history of coordinate planes

What is the slope of a vertical line?

• Zero

• One

• Undefined

• Negative

What is the slope of a horizontal line?

• Negative

• Undefined

• One

• Zero

How do vertical and horizontal lines relate in terms of direction?

• They do not move

• They move in the same direction

• They move diagonally

• They move in opposite directions

What is the slope of a line that moves over 1 and up 1?

• One

• Zero

• Negative one

• Undefined

What is the slope of a line that moves back over 1 and up 1?

• One

• Zero

• Undefined

• Negative one

Why are slopes of 1 and -1 not exactly negative reciprocals?

• Because they are both zero

• Because they are undefined

• Because they are just negatives of each other

• Because they are both positive

What is the slope of a line that goes up 3 and over 1?

• Zero

• One

• Three

• Negative one-third

What is the slope of a line that goes up 1 for every 3 it goes over?

• Negative one-third

• Three

• One

• Zero

Why do perpendicular slopes have to be negative reciprocals?

• Because they are both negative

• Because they are both positive

• Because they are undefined

• Because they move proportionally and in opposite directions