Finding domain and ranges for composition function

In summary: The thing is how do you graph 1/(x-1) + sqrt (x)?You can get a rough graph by doing it by hand. Pick values of x there are in the common domain for both functions (x ≥ 0, and x ≠ 1), the calculate the y-values.
  • #1
Coco12
272
0

Homework Statement



Find the domain and range of (f+g)(x)
Given that
F(x)= 1/(x-1) and g(x) = sqrt(x)

Homework Equations


The Attempt at a Solution


I added the two functions to get 1/(x-1) + sqrt(x)

To get domain, i look at the restrictive x values for both to get x greater than 0 and not equal to 1.
However how do i find the range?
 
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  • #2
Coco12 said:

Homework Statement



Find the domain and range of (f+g)(x)
Given that
F(x)= 1/(x-1) and g(x) = sqrt(x)

Another question let's say:
f(x) = x+3
G(x)= -x-4
Find the domain and range of (f*g)(x)

Homework Equations


The Attempt at a Solution


I added the two functions to get 1/(x-1) + sqrt(x)To get domain, i look at the restrictive x values for both to get x greater than 0 and not equal to 1.
However how do i find the range?
Graph both functions separately, preferably using different colors for each graph. Then, using a third color, or a marker pen, go over the parts of the two graphs for which x ≥ 0 and x ≠ 1. From that graph it should be evident what the range of the sum function is.
Coco12 said:
2) I multiplied f(x) and g(x) together to get -x^2-7x-12
My domain I got all real numbers, again how do i get the range?
The graph of the product function is a parabola that opens downward. You should already have a technique for finding the vertex of a parabola. Let's say that the vertex is at (a, b). Then the range will be {y| -∞ < y ≤ b}.

BTW, you misposted this problem in one of the physics sections. This is a precalc type problem, so I moved it to this section.
 
  • #3
is there another way to find the range without graphing it?
the answer is y less than -0.7886 or y greater than 2.2287.
How can you get to that precise of an answer when graphing it by hand??
 
  • #4
They're probably using a graphing calculator or some graphing utility.
 
  • #5
ImageUploadedByPhysics Forums1387135472.474199.jpg

For the second graph (f+g)(x)
The range in the back of the book says y less than .75 but u can see clearly in the graph that it is less than 1 ... What is going on?
 
  • #6
Mark44 said:
They're probably using a graphing calculator or some graphing utility.
ImageUploadedByPhysics Forums1387136498.132607.jpg

I drew the graph out it is just a sketch and would not be accurate on the range.. Are you expected to know precisely where it is?
 
  • #7
Coco12 said:
View attachment 64817
For the second graph (f+g)(x)
The range in the back of the book says y less than .75 but u can see clearly in the graph that it is less than 1 ... What is going on?
The graphs don't show the sum or difference of the two functions. Those (sum or difference) are the graphs of interest here.
 
  • #8
Mark44 said:
The graphs don't show the sum or difference of the two functions. Those (sum or difference) are the graphs of interest here.

The thing is how do you graph 1/(x-1) + sqrt (x)?
 
  • #9
You can get a rough graph by doing it by hand. Pick values of x there are in the common domain for both functions (x ≥ 0, and x ≠ 1), the calculate the y-values.

As I said before, they are probably using a graphing calculator or computer graphics package.
 
  • #10
So for example I would take 0.5 and plug it into the composite formula?
 
  • #11
But the range won't be accurate right?
 

Related to Finding domain and ranges for composition function

1. What is a composition function?

A composition function is a mathematical operation that combines two functions to create a new function. It is denoted by (f ∘ g)(x) and is read as "f of g of x." It means that the output of the inner function, g(x), becomes the input for the outer function, f(x).

2. How do you find the domain of a composition function?

To find the domain of a composition function, you must first find the domain of the inner function, g(x). Then, you must determine which values of x from g(x)'s domain will result in a real output for the outer function, f(x). The resulting values will be the domain of the composition function.

3. What is the range of a composition function?

The range of a composition function is the set of all possible output values from the function. To find the range, you must evaluate the composite function for different input values and determine the resulting output values.

4. How can you determine if a composition function is one-to-one?

A composition function is one-to-one if every input value has a unique output value. To determine this, you can graph the function and use the horizontal line test. If any horizontal line intersects the graph at more than one point, the function is not one-to-one.

5. Can a composition function have an empty domain or range?

No, a composition function cannot have an empty domain or range. Since the output of the inner function becomes the input for the outer function, there must be at least one value in the domain of the inner function that will result in a real output for the outer function.

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