00:01
Okay, so this question we want to show that your function f is equal to e to the x is not invertible when mapping from real numbers to real numbers.
00:10
So the reason why it is not invertible is because the function is not onto.
00:17
So if you draw the function f of x is equal to e to the x, you get a graph like this.
00:24
So this is x and this is your f.
00:29
So it's clearly not onto because your function.
00:32
Never gets any negative numbers here.
00:35
So it's not onto, so therefore you cannot invert it.
00:40
If you are dealing with functions that map from your real numbers to your real numbers.
00:47
If, however, you instead use your functions which map from the real numbers to the positive real numbers, so it's excluding negative, so every number up here, then it is a onto function.
01:01
So then it is a one -to -one, a one -to -one, and onto.
01:06
So to prove that it is one to one, once again you have to say, say if f of a is equal to f of b, what does this imply? it implies that e to the a is equal to e to the b...