Question

how do i know that a given function is one to one?

Answer 1

becasue for any given output, there is one and only one input that can create it

Answer 2

x^2 is not a one to one becuase:

y = 4; is produced from either x=2 or x=-2

Answer 3

we can know from graph

when u draw function you can do what we called ( test vertical line)
vertical line must intersection with one point of the graph of function

Answer 4

There can only be one image to one object.I will give you an example.The answer for
1×1=1
and not like 4 where you can have
2×2
or
4×1
This is just a rough idea.Hope you get it.