Math Problem Statement

Given f(x) = 9x and g(x) = 7x^2 + 4, find the following expressions: (a) (f ∘ g)(4), (b) (g ∘ f)(2), (c) (f ∘ f)(1), (d) (g ∘ g)(0).

Solution

To solve the problem, let us analyze the given functions and evaluate each composite expression step by step.

Given:

  • f(x)=9xf(x) = 9x
  • g(x)=7x2+4g(x) = 7x^2 + 4

(a) (fg)(4)(f \circ g)(4)

This means f(g(4))f(g(4)). First, calculate g(4)g(4): g(4)=7(42)+4=7(16)+4=112+4=116g(4) = 7(4^2) + 4 = 7(16) + 4 = 112 + 4 = 116 Now calculate f(116)f(116): f(116)=9(116)=1044f(116) = 9(116) = 1044 Thus, (fg)(4)=1044(f \circ g)(4) = 1044.


(b) (gf)(2)(g \circ f)(2)

This means g(f(2))g(f(2)). First, calculate f(2)f(2): f(2)=9(2)=18f(2) = 9(2) = 18 Now calculate g(18)g(18): g(18)=7(182)+4=7(324)+4=2268+4=2272g(18) = 7(18^2) + 4 = 7(324) + 4 = 2268 + 4 = 2272 Thus, (gf)(2)=2272(g \circ f)(2) = 2272.


(c) (ff)(1)(f \circ f)(1)

This means f(f(1))f(f(1)). First, calculate f(1)f(1): f(1)=9(1)=9f(1) = 9(1) = 9 Now calculate f(9)f(9): f(9)=9(9)=81f(9) = 9(9) = 81 Thus, (ff)(1)=81(f \circ f)(1) = 81.


(d) (gg)(0)(g \circ g)(0)

This means g(g(0))g(g(0)). First, calculate g(0)g(0): g(0)=7(02)+4=4g(0) = 7(0^2) + 4 = 4 Now calculate g(4)g(4): g(4)=7(42)+4=7(16)+4=112+4=116g(4) = 7(4^2) + 4 = 7(16) + 4 = 112 + 4 = 116 Thus, (gg)(0)=116(g \circ g)(0) = 116.


Final Results:

  • (a) (fg)(4)=1044(f \circ g)(4) = 1044
  • (b) (gf)(2)=2272(g \circ f)(2) = 2272
  • (c) (ff)(1)=81(f \circ f)(1) = 81
  • (d) (gg)(0)=116(g \circ g)(0) = 116

Let me know if you need a detailed explanation or help with related questions!

Relative Questions:

  1. What is the general formula for evaluating composite functions?
  2. How can we simplify the evaluation of quadratic functions like g(x)=7x2+4g(x) = 7x^2 + 4?
  3. What happens if f(x)f(x) or g(x)g(x) is not defined for certain values of xx?
  4. Can composite functions result in undefined values? When does this occur?
  5. How can we visualize the behavior of f(x)f(x) and g(x)g(x) on a graph?

Tip: Always calculate inner functions first when working with compositions to avoid mistakes!

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Math Problem Analysis

Mathematical Concepts

Function Composition
Algebra
Quadratic Functions

Formulas

f(x) = 9x
g(x) = 7x^2 + 4
(f ∘ g)(x) = f(g(x))
(g ∘ f)(x) = g(f(x))

Theorems

Function Composition Theorem

Suitable Grade Level

Grades 9-11