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# Recognizing functions from table

Checking whether a table of people and their heights can represent a function that assigns a height to a name. Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

• i don't understand how to tell whether a relation is a function or not.explain why or why not.maybe a video will help me.
• Okay i have officially decided that i am stupid could sombody please explain it to me in a different way?
• Ok, so basically, he is using people and their heights to represent functions and relationships. 1 person has his/her height. He/her could be the same height as someone else, but could never be 2 heights as once. This goes for the x-y values. An x value can have the same y-value correspond to it as another x value, but can never equal 2 y-values at once. Hopefully, you understand this.
• i still dont get what a relationship in a funtion is
• A relationship is saying that an input is related to this output in some way.

Functions are relationships that have one y per x.
(1 vote)
• So, a circle is not a function, correct?
• Yes, a circle is not a function. This is because it has 2 different y-values in the same x-position in some places. A easy way to see if something is a function is the vertical line test. You can imagine a vertical line going across the coordinate plane. If it ever intersects two points at once while it's going across, it's not a function. otherwise, it is.
• So just to clarify, you can have the same number in the domain, but not in the range?
• It's actually the other way around. Domain consists of the numbers you put into the function (x-values), and there can't be different values in the range (y-values) for the same x-value. There can be any amount of the same number for the range, no matter what the x-value is.
• Whoa whoa whoa, hold on...what if it's a different person with just the same name? What would happen then?
• You would either have to label by last initials, Nathan A. and Nathan K, or by numbers Nathan 1 and Nathan 2.
• Why does Sal place 5.11 higher than 5.6 on the graph?
• its not 5.11, it is 5 feet 11 inches. in that case, 5.11 has greater value on the graph.
• Does a linear function always HAVE to be a line, because on the Practice: Recognize Functions from graphs exercise it has problems that don't necessarily have lines and yet it still states that it is a linear function.
• Linear functions always create a line.
However, there are other types of equations and functions. I think the exercise is asking you to identify if the graph is a function, not necessarily a linear function.