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### Course: Pre-algebra>Unit 9

Lesson 5: Graphs of proportional relationships

# Proportional relationships: graphs

Learn how to tell proportional relationships by drawing graphs. Key idea: the graph of a proportional relationship is a straight line through the origin.

## Want to join the conversation?

• Excuse me any one there to answer my question ?
• In Sal says that -1/-2 is 1/2 and I get that but how is y=-1 if -1/-2 it wouldn't make -1. Wouldn't Y need to be 2?
• For that point, x = -2 and y = -1.

The -1/-2 calculation is just the ratio between y and x, and is 1/2.

My eyes get twisted with all the 1s and 2s, and I have to do a double-take sometimes.
• I still have know idea how to do this!
• maybe i can help. say this is a proportional relationship:
2 20
4 40
12 120
here is an equasion
y.r=X
you may have guessed that r=10
all you are doing is identifying that number, but this time with graphs to help you out.
• whats magenta?
• Magenta is the dark, purplish pink color in which the text regarding the first graph is written.
• Why does he call it proportional relationship? My school called it linear relationship, so I was really confused.
• A proportional relationship is one where there is multiplying or dividing between the two numbers. A linear relationship can be a proportional one (for example y=3x is proportional), but usually a linear equation has a proportional component plus some constant number (for example y=3x +4).
• how do you fin the rise and run on a graghp
• Find out the change in the y-value between two points, then the change in the x-value between the same 2 points. Use those measurements to solve (change in y)/(change in x).
• the last graph is wrong. You didn't graph (2,4) right, instead you graphed (2,3). Please be careful next time.
• This is a known error in the video. There is a correction box that pops up at about @. Always check for the correct box before posting that there is an error. Note: Correction boxes are not visible if you are watching in full screen mode.