Imagine you have two function machines, let's call them machine f and machine g. Each machine has its own rules, which are its function (f(x) and g(x)) and the raw materials it can process (its domain, and ). We can combine these two machines to create a new machine using addition or subtraction operations.
Df
Dg
Function Addition Visualization
Observe how the lines f(x)=x and g(x)=2 are added to become (f+g)(x)=x+2.
If we want to add function f and function g, we simply add the results from each function for the same value of x. The result is a new function we call (f+g).
(f+g)(x)=f(x)+g(x)
Important note: The combined machine (f+g) can only process raw materials (values of x) that can be processed by both original machines, f and g. So, the domain (domain of origin) of the function (f+g) is the intersection of the domain of f and the domain of g.
Df+g=Df∩Dg
This means that x must be a member of DfAND also a member of Dg.
The process is similar to addition. To subtract function g from function f, we subtract the result of g(x) from f(x) for the same value of x. The result is a new function (f−g).
(f−g)(x)=f(x)−g(x)
Its domain is also the same as for addition, namely the intersection of the domain of f and the domain of g. Why? Because again, the value of x must be processable by both initial functions before it can be subtracted.
We use the same functions as in the addition example:
f(x)=x2, Df={x∣x∈R}
g(x)=x+2, Dg={x∣x≥−2,x∈R}
Step1: Determine the resulting function from subtraction
(f−g)(x)=f(x)−g(x)=x2−x+2
Step2: Determine the domain of the resulting function
Its domain is the same as the domain of the addition result because the intersection rule is the same:
Df−g=Df∩Dg={x∣x≥−2,x∈R}
So, the resulting function from subtraction is (f−g)(x)=x2−x+2 with domain {x∣x≥−2,x∈R}.