A function is where for every X value there is only one y value. Also instead of writing "y=" you use "f(x)"

Ordered Pairs

{(0,12),(3,16),(0,20)} <--- that is an example of a non-function.

{(1,6),(2,9),(12,18)}<--- that is an example of a function.

{(1,2),(12,24),(25,50)} <---- that is another example of a function.

Equations

y=2x-12 <-- is a function

y=x²-12 <--- also a function

y=-12+2x<--- also a function

Graphs