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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=x2+1, gx=2x2+3

Short Answer

Expert verified

Part(a)f∘g=4x4+12x2+10anddomainis-∞,∞Part(b)g∘f=2x4+4x2+5anddomainis-∞,∞Part(c)f∘f=x4+2x2+2anddomainis-∞,∞Part(d)g∘g=8x4+24x2+21anddomainis-∞,∞

Step by step solution

01

Part (a)  Step 1. Given Information. 

We have given,

fx=x2+1, gx=2x2+3

02

Part (a)  Step 2. Concept. 

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

f ∘ g=fgx

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

03

Part (a) Step 2. Explanation.

We have given,

fx=x2+1, gx=2x2+3

Using definition of the composite function,

localid="1647491500448" f ∘ g=fgx=f2x2+3=(2x2+3)2+1=4x4+12x2+10

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=x2+1, gx=2x2+3isf ∘ g=4x4+12x2+10and domain is-∞,∞.

05

Part (b) Step 1. Explanation. 

We have given,

fx=x2+1, gx=2x2+3

Using definition of the composite function,

g ∘ f=gfx=gx2+1=2x2+12+3=2x4+4x2+5

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, composition of the functions fx=x2+1, gx=2x2+3is g ∘ f=2x4+4x2+5and domain is-∞,∞.

07

Part (c)  Step 1. Explanation. 

We have given,

fx=x2+1, gx=2x2+3

Using definition of the composite function,

f ∘ f=ffx=fx2+1=x2+12+1=x4+2x2+2

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:-∞,∞

08

Part (c) Step 2. Conclusion.

Hence, composite function of the function fx=x2+1, gx=2x2+3is f ∘ f=x4+2x2+2and domain is-∞,∞.

09

Part (d) Step 1. Explanation. 

We have given,

fx=x2+1, gx=2x2+3

Using definition of the composite function,

g ∘ g=ggx=g2x2+3=22x2+32+3=8x4+24x2+21

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 function fx=x2+1, gx=2x2+3isg ∘ g=8x4+24x2+21and domain of the function is-∞,∞.

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