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91Ó°ÊÓ

For the given functions f and g, find:

a)f∘gb)g∘fc)f∘fd)g∘g

State the domain of each composite function.

fx=-x and gx=2x-4

Short Answer

Expert verified

Part(a)f∘g=-2x+4anddomainis-∞,∞Part(b)g∘f=-2x-3anddomainis-∞,∞Part(c)f∘f=xanddomainis-∞,∞Part(d)g∘g=4x-12anddomainis-∞,∞

Step by step solution

01

Part (a) Step 1. Given Information.

We have given,

fx=-x and gx=2x-4

02

Part (a)  Step 2. Concept.

A function which is depends on any other function we can call it as composite function.

f ∘ g(x)=fgx

Domainis the set of all input values where function is well defined and objective.

03

Part (a) Step 3. Explanation.

We have given,

fx=-x and gx=2x-4

Using definition of the composite function,

(f∘g)(x)=f(g(x))=f(2x-4)=-(2x-4)=-2x+4

We have given functions f and g both are polynomial functions so the domain of both functions is set of real numbers.

Therefore domain of the composite function is also the set of real numbers.

Domain:-∞,∞

04

Part (a) Step 4. Conclusion.

Hence, composite function of the functions fx=-x and gx=2x-4is f ∘ g=-2x+4and domain is-∞,∞.

05

Part (b) Step 1. Explanation

We have given,

fx=-x and gx=2x-4

Using definition of the composite function,

g∘f(x)=g(f(x))=g(-x)=2(-x)-3=-2x-3

We have given functions f and g both are polynomial functions so the domain of both functions is set of real numbers.

Therefore domain of the composite function is also the set of real numbers.

Domain:-∞,∞

06

Part (b) Step 2. Conclusion.

Hence, composite function g∘fof the functionsfx=-x and gx=2x-4isg∘f=-2x-3and domain of the function is-∞,∞.

07

Part (c)  Step 1. Explanation.

We have given,

fx=-x and gx=2x-4

Using definition of the composite function,

(f∘f)(x)=f(f(x))=f(-x)=-(-x)=x

We have given functionsf and g both are polynomial functions so the domain of both functions is set of real numbers.

Therefore domain of the composite function is also the set of real numbers.

Domain:-∞,∞

08

Part (c) Step 2. Conclusion.

Hence, composite function of fx=-x with itself isf∘f=xand domain of the function is,-∞,∞.

09

Part (d) Step 1. Explanation.

We have given,

fx=-x and gx=2x-4

Using definition of the composite function,

(g∘g)(x)=g(g(x))=g(2x-4)=2(2x-4)-4=4x-8-4=4x-12

We have given functions f and g both are polynomial functions so the domain of both functions is set of real numbers.

Therefore domain of the composite function is also the set of real numbers.

Domain:-∞,∞

10

Part (d) Step 2. Conclusion.

Hence, composite function of the functions fx=-x and gx=2x-4is

g∘g=4x-12and domain of the composite function is,-∞,∞.

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