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

Question

amistre64 · Answer

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

amistre64 · Answer

x^2 is not a one to one becuase:

y = 4; is produced from either x=2  or   x=-2

anonymous · Answer

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

anonymous · Answer

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.