Since it's a function f(x)=x, this line goes on forever!!!
Thus, it will continue going longer (aka increasing in the x-direction) and grow taller (aka increasing in the y direction).
Thus the domain and range is
D={xER)
R=(yER)
which basically means, "x is an element of the Real number sets" (aka x is a real number, but other than that, there's no other restriction)
