Question

what is function?

Answer 1

A function is a verb. It DOES something. You input a number, then you DO SOMETHING to that input (multiply it, add it, divide it, take square root of it...etc.).

The input is usually x , the output is usually y.
When you graph all (x,y) points, you have some sort of a curve called a graph. :)

Answer 2

a function is defined as a special type of relation; one on which the input produces only one given output

Answer 3

a function is NOT an equation; but equations can define how a function operates :)