How to find the domain and range of y=|x| ?

D: (-inf, +inf)
R: [0, +inf)

That equation is the parent function of the absolute value function. To find domain, move from left to right. Look at the x-values and where the graph goes. To find range, move from bottom to top and look at the y-values. I recommend using a stick/pencil and moving it along the graph.