Which relation is a function?

A.
{(1, 2), (1, 5), (1, –1), (1, 4)}

B.
{(8, –1), (2, –1), (3, 8), (2, 5}

C.
{(–3, 4), (–2, 5), (0, 9), (0, 12)}

D.
{(7, 12), (1, –5), (3, –10), (2, –5)}

Question

Which relation is a function?	
 
 A.
{(1, 2), (1, 5), (1, –1), (1, 4)}
 
 B.
{(8, –1), (2, –1), (3, 8), (2, 5}
 
 C.
{(–3, 4), (–2, 5), (0, 9), (0, 12)}
 
 D.
{(7, 12), (1, –5), (3, –10), (2, –5)}

mertsj · Answer

A function is a relation in which no two ordered pairs have the same first number.

mertsj · Answer

So which one is it?

ash2326 · Answer

A relation {(x1, y1) (x2, y2).....(xn, yn)} is a function if for every x there is one value of y
Example
(1, 2) (2, 3)
Here for 1 $\to$ 2
and for 2$\to$ 3
so there is a one element of each x, therefore it's a function
If on the other hand, we had the relation
$$\{(1, 2), (2,3), (1, 4)\}$$
here for 1$\to$2
and again for 1$\to$4 so there are two values of y for 1, so this is not a function. Do you understand this???

2yoututu11 · Answer

idk

ash2326 · Answer

@2yoututu11 Did you answer for my question or @Mertsj ?

ash2326 · Answer

Did  you understand?

anonymous · Answer

maybe this will help if you are still confused:

a function must be "1 to 1" or "many to 1"

it cant be "1 to many"

eg it cant map 2 to -1 and also map 2 to 5

2yoututu11 · Answer

Yeaa I found it now thank you@ Ash2326

ash2326 · Answer

Welcome @2yoututu11 :D