The vertical line test is a method that is used to determine whether a given relation is a function or not. ... The vertical line test supports the definition of a function. That is, every x-value of a function must be paired to a single y-value.
The identity property means that whatever you put in is whatever comes out. Notice that if we multiply 1 with any number, we get that number back. So multiplying by 1 is the identity property of multiplication.
