Answer:
Second and fourth graph represent invertible functions.
Step-by-step explanation:
According to the theory of functions, a function is invertible if it's one-to-one and surjective.
In addition, there's a graphic test called "horizontal line test". This test is used to know if a function is one-to-one. It consist in drawing an horizontal line across the graph, if the line intercept the function at one point, then that function is one-to-one, if the line intercept the function at two points, then that function is not one-to-one. And, if the function is one-to-one, then it can be invertible.
So, in the given graph, if we draw a horizontal line on each function, the first and third function aren't one-to-one, so they aren't invertible.
Therefore, by the horizontal line test, the second and fourth functions are one-to-one and they are invertible.
