Relations and functions are very closely related. While all functions are relations, not all relations are functions. That's because functions are a special subset of relations. You can think of a relation as a set containing pairs of related numbers. For example, {(0,0), (1,1), (2,4), (3,9), (4,16)}represents a relation. There are five pairs of numbers. In each pair, the values of the second numbers (known as the range) are dependent upon the values of the first numbers (known as the domain). You can also think of the first number in each pair to be the x value and the second number to be the y value. In other words, y is dependent upon x. So, what makes a relation a function? For a relation to be a function, there must be one and only one y value for each x value. If there are two pairs of numbers that have the same x value but different y values, then the relation is NOT a function. In the above example, the domain is between zero and four, inclusive. Because each x value is unique and has only one corresponding y value, the relation is, in fact, a function. The function is y = x2, which can also be written f(x) = x2.
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Not every relation is a function. But every function is a relation. Function is just a part of relation.
A function is a relation whose mapping is a bijection.
If a vertical line intersects the graph at more than one point then it is not a function.
No. A relation is not a special type of function.
Good question. A relation is simply that; any x-value to create any y-value. A function, however, cannot be defined for multiple values of x. In other words, for a relation to be a function, it must have singular values for all x within its domain.