Mathematics for IGCSE & O level - Functions (Section 2 - No. 22)
Which of the following represents a function?
A mapping of one x-value to two y-values
A relationship where each input has only one output
A relationship where one y-value can be related to many x-values
A graph that fails the vertical line test.
Forklaring
A function must have a single output value for each input value.