Domain of a composite function

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Homework Help Overview

The discussion revolves around finding the domain of the composite function h(g(x)), where the functions involved are f(x)=4x-1, g(x)=3-2x^2, and h(x)=sqrt(x+5). Participants are exploring the necessary conditions for the domains of these functions to determine the valid inputs for the composite function.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the need to identify the domains of the individual functions f, g, and h. There is uncertainty about what values need to be considered from g(x) when determining the domain of h(g(x)). Some participants question the assumptions regarding the values of x that are permissible for g(x) and how they affect h(g(x)).

Discussion Status

The discussion is ongoing, with participants providing insights into the definitions of the domains of the functions involved. Some have suggested methods for checking the conditions under which g(x) yields values suitable for h(x). There is a general sense of progress as participants clarify their understanding of the composite function's domain.

Contextual Notes

Participants are grappling with the specific constraints of the functions, particularly regarding the square root function h(x) and its implications for the values produced by g(x). There is mention of needing to solve inequalities related to the outputs of g(x) to ensure they fit within the domain of h(x).

ilii
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Homework Statement


Given the Functions
f(x)=4x-1
g(x)=3-2x^2
h(x)= sqrt (x+5)

What is the domain of h(g(x))?

Homework Equations



the subject is finding the domain of a composite function

The Attempt at a Solution


I don't understand what I have to 'bring over' from g(x). I think x cannot equal zero for g(x). If someone could post a structured list of steps I need to take to find the domain of a composite function, it would be much appreciated.

thank you
 
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The domain of a composite function (f \circ g)(x)=f(g(x)) is defined as D(f\circ g)=\{x \epsilon D(g) | g(x) \epsilon D(f) \}. So you should find the domains of f and g and check that for what subset of the domain of g, it gives values in the domain of f.
 
ilii said:

Homework Statement


Given the Functions
f(x)=4x-1
g(x)=3-2x^2
h(x)= sqrt (x+5)

What is the domain of h(g(x))?

Homework Equations



the subject is finding the domain of a composite function

The Attempt at a Solution


I don't understand what I have to 'bring over' from g(x). I think x cannot equal zero for g(x).

thank you

Why do you think that? ##g(x)## is just a polynomial. What' wrong with ##g(0)##?
What is the formula for ##h(g(x))##? What values of ##x## work in that?
 
The domain of square root is "numbers greater than or equal to 0". h(x)= sqrt(x- 5) so the domain of h is "x- 5\ge 0 or x\ge 5. That means that g(x)= 3- 2x^2 must give only values greater than or equal to 5. Can you solve 3- 2x^2\ge 5?
 
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thanks everyone I understand it much better now :D
 

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