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If f(x)=4x+3 and g(x)= the square root of x-9, which is true? 2 is in the domain of f of g or 2 is not in the domain of f of g?

User Thriveni
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Answer:

2 is not in the domain of f of g

Explanation:

* Lets revise at first the meaning of f of g (composite function)

- A composite function is a function that depends on another function

- A composite function is created when one function is substituted into

another function

- Example:

# f(g(x)) is the composite function that is formed when g(x) is

substituted for x in f(x).

- In the composition (f ο g)(x), the domain of f becomes g(x)

* Now lets solve the problem

∵ f(x) = 4x + 3

∵ g(x) = √(x - 9)

- Lets find f(g(x)), by replacing x in f by g(x)

∴ f(g(x)) = f(√(x - 9)) = 4[√(x - 9)] + 3

∴ f(g(x)) = 4√(x - 9) + 3

∵ The domain of f is g(x)

- The domain of the function is the values of x which make the

function defined

∵ There is no square root for negative values

∴ x - 9 must be greater than or equal zero

∵ x - 9 ≥ 0 ⇒ add 9 for both sides

∴ x ≥ 9

∴ The domain of f of g is all the real numbers greater than or equal 9

∴ The domain = {x I x ≥ 9}

∵ 2 is smaller than 9

∴ 2 is not in the domain of f of g

User DreamsOfHummus
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