Math Problem Statement

Given the definitions of f(x) = 3x^2 + 6x - 13 and g(x) = 2x + 4, find the value of (f ∘ g)(-4).

Solution

We are given two functions, f(x)f(x) and g(x)g(x), and we are asked to find the value of (fg)(4)(f \circ g)(-4), which represents the composition of functions evaluated at 4-4.

Step 1: Understand the composition of functions

The notation (fg)(x)(f \circ g)(x) means f(g(x))f(g(x)), so we first need to evaluate g(x)g(x) at 4-4 and then substitute that result into f(x)f(x).

Step 2: Evaluate g(x)g(x) at 4-4

We are given: g(x)=2x+4g(x) = 2x + 4 Substitute x=4x = -4: g(4)=2(4)+4=8+4=4g(-4) = 2(-4) + 4 = -8 + 4 = -4

Step 3: Evaluate f(x)f(x) at the result from Step 2

Now we substitute g(4)=4g(-4) = -4 into f(x)f(x). The function f(x)f(x) is given by: f(x)=3x2+6x13f(x) = 3x^2 + 6x - 13 Substitute x=4x = -4: f(4)=3(4)2+6(4)13f(-4) = 3(-4)^2 + 6(-4) - 13 f(4)=3(16)+(24)13=482413=11f(-4) = 3(16) + (-24) - 13 = 48 - 24 - 13 = 11

Final Answer:

(fg)(4)=11(f \circ g)(-4) = 11

Would you like more details on any step or have questions about the method?

Here are five related questions to explore further:

  1. How does function composition differ from simple addition or multiplication of functions?
  2. What are the domain and range considerations for composed functions like (fg)(x)(f \circ g)(x)?
  3. How can we decompose a composed function into simpler functions?
  4. What is the geometric interpretation of composing functions?
  5. Can you solve for (gf)(x)(g \circ f)(x) instead, and how does it differ?

Tip: Always evaluate the inner function first when dealing with composition to avoid confusion.

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Math Problem Analysis

Mathematical Concepts

Function Composition
Algebra
Quadratic Functions

Formulas

f(x) = 3x^2 + 6x - 13
g(x) = 2x + 4
Function composition: (f ∘ g)(x) = f(g(x))

Theorems

No specific theorem involved, but function composition is the main technique.

Suitable Grade Level

Grades 9-12