To find the domain of this function we need to find all
x such that 
21
1
1
1
4
x
x
+
− ≤
≤
+ Since the quantity in the middle is always positive,
we need to find all x such that 
1
2
1
1
4
x
x
+
≤
+
, i e , all x such that 2x + 1 ≤ 1 + 4x