Question

What makes a function a function?

Answer 1

depends...algebraically or graphically?

Answer 2

in algebra you know it's a function when the exponent of y is just 1

Answer 3

for example

y = x^2 + 1

y = x - 1

etc

Answer 4

graphs

Answer 5

do a vertical line test
suppose that's the graph

Answer 6

draw some vertical lines

as you can see the lines touch the graph once only