Answer:
Because the linear functions have the form y = mx + b
Step-by-step explanation:
The typical linear function has the following form:
y = mx + b
Where m and b are constant values, so an example of a linear function is:
y = 3x + 5
Now, the domain is the set of all the possibles values that the variable x can take and the range is all the possible values that the value y can take given the values of x.
Since it has the form y = 3x + 5 it is possible to replace x by any Real number and get for y another real number.