Solution
State whether it is one-to-one.
If a function has no two ordered pairs with different first coordinates and the same second coordinate, then the function is called one-to-one.
In a one-to-one function, given any y there is only one x that can be paired with the given y.
A graph of a function can also be used to determine whether a function is one-to-one using the horizontal line test:
If each horizontal line crosses the graph of a function at no more than one point, then the function is one-to-one.
Consider the graphs of the following two functions:
Hence
Graph 4 is not a one to one function
Graph 5 is a one to one function
Graph 6 is a one to one function
Therefore graph 4 is NO, graph 5 and 6 are both yes