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# How do you know a relationship b/w x and y is a function?

i'm really bad at algebra.... *sigh*

apparantly the dictionary meaning for a "function" is:

a cosistent, predictable, relationship between the independant and dependant variable...

but i cant figure out all that mathematical jib-jab gibberish.

### 4 Answers

- 1 decade agoFavorite Answer
basically, think of a function as a machine:

take this an an example: f(x) = 2x +3

see the x in brackets?

if x = 1, then f(1) = 2(1) + 3 = 5

if x = 2, then f(2) = 2(2) + 3 = 7

if x = 3, then f(3) = 2(3) + 3 = 9

see whats happening? the answer DEPENDS on number inputted in the brackets.

so therefore, the definition you quoted "a consistent, predictable, relationship between the independant and dependant variable" is true.

- 1 decade ago
The people below gave you right answers but if you ask me it is too complicated.

know this.

After getting a set of coordinates (x and y) check them all and make sure the x coordinate doesn't repeat itself if so it is not a function, however the y coordinate can repeat itself and that relation can still be a function for example

(x , y)

2, 3

3, 4 Not a function

4, 3

2, 5

this relation is not a function

because on the x coordinate

you have a number thatt repeats itself

and that number is 2.

NOTE= as long as tha X doesn't repeat itself then that relation is a function.

(x,y)

2,3

4,4

6,4 this is a function because the x coordinate didn't repeat itself.

0,3

I hope this helps you. good luck

- 1 decade ago
y(x) = x is a function because for every value of x there is only one value of y.

i.e. y(x) = 2x

when x = 2 then y = 4. If you know x then you can find y