What is the domain of
y=x
We can also write y = x as f(x) = x because f(x) = y and vice-versa since both represent a function.
In your case, y = x is a linear function because it forms a LINE PICTURE when graphed on the xy-plane. The line y = x goes through the origin or this point (0,0) from the first quadrant through the point (0,0) and into the third quadrant.
You can safely replace x with any real number of choice to find y values.
So, the domain for the line y = x, is:
ALL REAL NUMBERS.
Is this clear?