How do you tell if a relation is a function or not?

Question

geerky42 · Answer

Have you heard of vertical line test?

geerky42 · Answer

No? this webpage may help: http://www.mathwarehouse.com/algebra/relation/vertical-line-test.php

igreen · Answer

A relation is not a function when the x coordinate is repeated twice.

anonymous · Answer

What about ones without graphs, for example this takes place instead of a graph as an answer choice. 

 Which relation is a function?
This is one of the answer choices. 
@geerky42

igreen · Answer

It is a relation when each 'x' value is with one value of 'y'.

You can't have a stray 'x' or 'y' value.

anonymous · Answer

I think this one answers that question...

geerky42 · Answer

single value of x cannot have more than two y values, otherwise it's not function

geerky42 · Answer

For example, first one you attached, x value, 5 contains both y values, 1 and 2, so it's not function.

Is this clear?

anonymous · Answer

er...no. sorry.

anonymous · Answer

well actually there are two ways..
i_ vertical line test thatz suitable when graph is given or if u draw the graph...

There are two conditions for a relation to become a fun..
1 Domain of Relation=Set A
2.No first element should be repeated in short for one value of domain two diff answers are not possible....

anonymous · Answer

i hope u got it???

anonymous · Answer

Domain? How do you find the domain?

anonymous · Answer

well domain is the set of those values at which function is not un-defined...

& it is equal to the set of 1st elements of the ordered pairs...

anonymous · Answer

i hope it helps....