Math Problem Statement

Evaluate the composite function, where

f(x) = 2x + 3, and g(x) = x2 − 4x.

(g ∘ f)(

sqrt 3

)

Solution

To evaluate the composite function (gf)(3)(g \circ f)(\sqrt{3}), we'll break it down step by step.

Step 1: Understand the composite function

The composite function (gf)(x)(g \circ f)(x) means that we first apply the function f(x)f(x), and then use the result of f(x)f(x) as the input to the function g(x)g(x). Mathematically, this can be written as: (gf)(x)=g(f(x))(g \circ f)(x) = g(f(x))

Step 2: Apply f(x)f(x) to 3\sqrt{3}

Given that f(x)=2x+3f(x) = 2x + 3, let's substitute 3\sqrt{3} into f(x)f(x): f(3)=2(3)+3=23+3f(\sqrt{3}) = 2(\sqrt{3}) + 3 = 2\sqrt{3} + 3

Step 3: Use the result in g(x)g(x)

Now, substitute f(3)=23+3f(\sqrt{3}) = 2\sqrt{3} + 3 into g(x)g(x). The function g(x)=x24xg(x) = x^2 - 4x, so: g(23+3)=(23+3)24(23+3)g(2\sqrt{3} + 3) = (2\sqrt{3} + 3)^2 - 4(2\sqrt{3} + 3)

Step 4: Simplify the expression

We'll first expand both terms:

Expand (23+3)2(2\sqrt{3} + 3)^2:

(23+3)2=(23)2+2(23)(3)+32=12+123+9=21+123(2\sqrt{3} + 3)^2 = (2\sqrt{3})^2 + 2(2\sqrt{3})(3) + 3^2 = 12 + 12\sqrt{3} + 9 = 21 + 12\sqrt{3}

Expand 4(23+3)-4(2\sqrt{3} + 3):

4(23+3)=8312-4(2\sqrt{3} + 3) = -8\sqrt{3} - 12

Step 5: Combine terms

Now combine the two results: g(23+3)=(21+123)+(8312)=2112+12383g(2\sqrt{3} + 3) = (21 + 12\sqrt{3}) + (-8\sqrt{3} - 12) = 21 - 12 + 12\sqrt{3} - 8\sqrt{3} =9+43= 9 + 4\sqrt{3}

Final Answer:

(gf)(3)=9+43(g \circ f)(\sqrt{3}) = 9 + 4\sqrt{3}

Would you like further clarification or details on any step?


Here are 5 related questions:

  1. What is the general process for evaluating composite functions?
  2. How do you simplify expressions with square roots?
  3. How does the distributive property apply to expanding terms like (23+3)2(2\sqrt{3} + 3)^2?
  4. What is the domain of the composite function gf(x)g \circ f(x)?
  5. Can composite functions ever be non-existent for certain inputs?

Tip: When expanding binomials like (a+b)2(a + b)^2, remember to use the formula a2+2ab+b2a^2 + 2ab + b^2 for faster calculations.

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Math Problem Analysis

Mathematical Concepts

Functions
Composite Functions
Algebra
Square Roots

Formulas

f(x) = 2x + 3
g(x) = x^2 - 4x
(g ∘ f)(x) = g(f(x))
(a + b)^2 = a^2 + 2ab + b^2

Theorems

Function Composition

Suitable Grade Level

Grades 10-12