The range of a function is all possible output, or yy, values. The domain is all possible input, or xx, values. In the case of y=xy=x, both the range and domain are all real numbers.You can plug in all sorts of negative and positive xx and yy values; there are no restrictions. So, in interval notation
The range: (-∞, ∞)
The domain: (-∞, ∞)
Note the round brackets ( ) because since infinity isn't a number, the functions can't be defined there. The functions just tend to infinity as the xx and yy values get infinitely large or infinitely small.
The function y=xy=x is an interesting case of domain and range because the domain and range values are always the same. In other words, since yy always equals xx, the input values always equal the output values.y=xy=x is also actually just the graph of a straight line, with a slope of 1 and a yy-intercept at (0,0). You'll see that all points will have equivalent values, so some points on the line would be (4,4) or (-178, -178). To graphically observe the equivalence of the domain and range, here is a graph of the line:
