This week we have learned about functions, to identity functions, there’s some rules. First, the input x cannot be the same, they all should be different in order to get different outcomes, one input x cannot be resulted to many output, it can only resulted to one output y. but sometimes the output y will be resulted from numbers of input x. Here’s is an example:

Moreover, the vertical line test can be used to determine whether a graph represents a function. A vertical line includes all points with a particular $x$ value. The $y$ value of a point where a vertical line intersects a graph represents an output for that input $x$ value. If we can draw any vertical line that intersects a graph more than once, then the graph does not define a function because that $x$ value has more than one output. A function has only one output value for each input value.