Math Problem Statement

For f(x)= 3-x and g(x)= 2x^2 + x +4 find the following functions. B. (g o f)(x) c. (f o g)(2) d. (g o f)(2)

Solution

Let's break down each part of your question step by step.

Given Functions:

  • f(x)=3xf(x) = 3 - x
  • g(x)=2x2+x+4g(x) = 2x^2 + x + 4

B. Find (gf)(x)(g \circ f)(x):

The composition (gf)(x)(g \circ f)(x) means we are plugging f(x)f(x) into g(x)g(x). This is the same as:

(gf)(x)=g(f(x))(g \circ f)(x) = g(f(x))

Substitute f(x)=3xf(x) = 3 - x into g(x)g(x):

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

Now, substitute 3x3 - x into g(x)g(x):

g(3x)=2(3x)2+(3x)+4g(3 - x) = 2(3 - x)^2 + (3 - x) + 4

Let's expand this expression:

(3x)2=96x+x2(3 - x)^2 = 9 - 6x + x^2 g(3x)=2(96x+x2)+(3x)+4g(3 - x) = 2(9 - 6x + x^2) + (3 - x) + 4 g(3x)=2(9)2(6x)+2(x2)+3x+4g(3 - x) = 2(9) - 2(6x) + 2(x^2) + 3 - x + 4 g(3x)=1812x+2x2+3x+4g(3 - x) = 18 - 12x + 2x^2 + 3 - x + 4 g(3x)=2x213x+25g(3 - x) = 2x^2 - 13x + 25

So, (gf)(x)=2x213x+25(g \circ f)(x) = 2x^2 - 13x + 25.

C. Find (fg)(2)(f \circ g)(2):

The composition (fg)(2)(f \circ g)(2) means we need to first evaluate g(2)g(2), and then apply ff to that result. So we do the following:

  1. Evaluate g(2)g(2): g(2)=2(2)2+2+4g(2) = 2(2)^2 + 2 + 4 g(2)=2(4)+2+4=8+2+4=14g(2) = 2(4) + 2 + 4 = 8 + 2 + 4 = 14

  2. Now, apply ff to g(2)=14g(2) = 14: f(14)=314=11f(14) = 3 - 14 = -11

So, (fg)(2)=11(f \circ g)(2) = -11.

D. Find (gf)(2)(g \circ f)(2):

To find (gf)(2)(g \circ f)(2), we first need to evaluate f(2)f(2), and then apply gg to that result.

  1. Evaluate f(2)f(2): f(2)=32=1f(2) = 3 - 2 = 1

  2. Now, apply gg to f(2)=1f(2) = 1: g(1)=2(1)2+1+4=2+1+4=7g(1) = 2(1)^2 + 1 + 4 = 2 + 1 + 4 = 7

So, (gf)(2)=7(g \circ f)(2) = 7.

Summary of Results:

  • (gf)(x)=2x213x+25(g \circ f)(x) = 2x^2 - 13x + 25
  • (fg)(2)=11(f \circ g)(2) = -11
  • (gf)(2)=7(g \circ f)(2) = 7

Would you like more details on any of these steps or have other questions?


Here are 5 related questions to explore further:

  1. How do you find the composition of functions in general?
  2. What would happen if we had more complex functions for f(x)f(x) and g(x)g(x)?
  3. How can the composition of functions be used in real-world scenarios?
  4. What is the difference between (gf)(x)(g \circ f)(x) and (fg)(x)(f \circ g)(x)?
  5. How do you handle compositions involving higher-degree polynomials?

Tip: When composing functions, always be careful to substitute the entire expression of one function into the other and simplify step by step.

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Math Problem Analysis

Mathematical Concepts

Function Composition
Algebra
Quadratic Functions

Formulas

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

Theorems

Function Composition Theorem

Suitable Grade Level

Grades 9-11