if f(x)=2x-3 and fg(x)=2x+1,find g(x)

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sciencesolve | Teacher | (Level 3) Educator Emeritus

Posted on

You should notice that the composition of the functions f and g is a linear function.

You need to remember how to compose two functions such that:

`(fog)(x) = f(g(x))`

Since `f(x) = 2x - 3` , you should substitute g(x) for x such that:

`f(g(x)) = 2g(x) - 3`

The problem provides the information that `f(g(x)) = 2x+1` , hence, you should set the equations 2g(x) - 3 and 2x+1 equal such that:

`2g(x) - 3 = 2x + 1 =gt 2g(x) = 2x + 1 + 3`

`2g(x) = 2x + 4`

Dividing by 2 yields:

`g(x) = x + 2`

Hence, evaluating the function g(x) under the given conditions yields `g(x) = x + 2` .

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dodafone's profile pic

dodafone | Student, Undergraduate | (Level 1) eNoter

Posted on

first we see that g(x) should be a linear polynomial as only then fg(x) will come out to be linear 

let g(x)=ax + b

fg(x)=2(ax +b) -3

=x(2a) +(2b-3) which is given equal to 2x +1

on comparing we get 
2a=2        a=1

2b-3=1     b=2

g(x)=x+2

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