Math Problem Statement

Use f(x) = 2x − 4 and g(x) = 5 − x2 to evaluate the expression. find f o g (-2) and g o f (-2)

Solution

To solve this problem, we need to evaluate two function compositions: fg(2)f \circ g (-2) and gf(2)g \circ f (-2). Let’s break it down step by step.

Step 1: Find fg(2)f \circ g (-2)

The notation fg(2)f \circ g (-2) means f(g(2))f(g(-2)). So, we need to first find g(2)g(-2) and then substitute that result into the function f(x)f(x).

  1. Find g(2)g(-2): g(x)=5x2g(x) = 5 - x^2 Substituting x=2x = -2: g(2)=5(2)2=54=1g(-2) = 5 - (-2)^2 = 5 - 4 = 1

  2. Find f(g(2))=f(1)f(g(-2)) = f(1): The function f(x)=2x4f(x) = 2x - 4. Now, substitute x=1x = 1: f(1)=2(1)4=24=2f(1) = 2(1) - 4 = 2 - 4 = -2

Thus, fg(2)=2f \circ g(-2) = -2.

Step 2: Find gf(2)g \circ f (-2)

The notation gf(2)g \circ f (-2) means g(f(2))g(f(-2)). First, we need to find f(2)f(-2), and then substitute that result into the function g(x)g(x).

  1. Find f(2)f(-2): f(x)=2x4f(x) = 2x - 4 Substituting x=2x = -2: f(2)=2(2)4=44=8f(-2) = 2(-2) - 4 = -4 - 4 = -8

  2. Find g(f(2))=g(8)g(f(-2)) = g(-8): The function g(x)=5x2g(x) = 5 - x^2. Now, substitute x=8x = -8: g(8)=5(8)2=564=59g(-8) = 5 - (-8)^2 = 5 - 64 = -59

Thus, gf(2)=59g \circ f(-2) = -59.

Final Answers:

  1. fg(2)=2f \circ g (-2) = -2
  2. gf(2)=59g \circ f (-2) = -59

Would you like more details or have any questions about the steps? Here are 5 related problems for further practice:

  1. Evaluate fg(3)f \circ g(3) for the same functions.
  2. Evaluate gf(0)g \circ f(0).
  3. Find f(g(x))f(g(x)) in general form.
  4. Find g(f(x))g(f(x)) in general form.
  5. Solve f(x)=g(x)f(x) = g(x) for xx.

Tip: When working with function compositions, always apply the inner function first before substituting its result into the outer function.

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Math Problem Analysis

Mathematical Concepts

Function Composition
Algebra
Quadratic Functions

Formulas

f(x) = 2x - 4
g(x) = 5 - x²

Theorems

Function Composition Theorem

Suitable Grade Level

Grades 9-11