Math Problem Statement

Find the composite functions f ◦ g, g ◦ f and their domains. Also, find the inverse of the function h(x) = √(x² + 28) - 5 and its domain.

Solution

Let's break down the tasks step by step based on the given image.

1. Functions and their Domains:

  • f(x)=9x2+6f(x) = 9x^2 + 6, where the domain Mf=[,1]M_f = [-\infty, -1].
  • g(x)=13x6g(x) = -\frac{1}{3} \sqrt{x - 6}, where the domain Mg=[7,[M_g = [7, \infty[.

The task is to find the composition of these functions, along with the associated domains, and also the inverse of another function h(x)h(x).

2. Composition of Functions:

You are asked to compute fgf \circ g and gfg \circ f, then find the domains MfgM_{f \circ g} and MgfM_{g \circ f}.

a. Finding fgf \circ g and its domain:

  • fg(x)=f(g(x))f \circ g(x) = f(g(x)), which means you substitute g(x)g(x) into f(x)f(x).
  • Given that g(x)=13x6g(x) = -\frac{1}{3} \sqrt{x - 6}, substitute this into f(x)=9x2+6f(x) = 9x^2 + 6.
  • Find the domain where this composition is valid. It will be the intersection of the domains of ff and gg, considering the range of g(x)g(x) must fit within the domain of f(x)f(x).

b. Finding gfg \circ f and its domain:

  • gf(x)=g(f(x))g \circ f(x) = g(f(x)), which means you substitute f(x)f(x) into g(x)g(x).
  • Substitute f(x)=9x2+6f(x) = 9x^2 + 6 into g(x)=13x6g(x) = -\frac{1}{3} \sqrt{x - 6}.
  • Similarly, find the domain MgfM_{g \circ f}, ensuring the input of f(x)f(x) leads to valid outputs in the domain of g(x)g(x).

3. Inverse of h(x)h(x):

The function h(x)=x2+285h(x) = \sqrt{x^2 + 28} - 5, with x[0,2]x \in [0, 2], is given. You are asked to find the inverse function h1(x)h^{-1}(x) and its domain Mh1M_{h^{-1}}.

  • To find the inverse, solve y=x2+285y = \sqrt{x^2 + 28} - 5 for xx in terms of yy.
  • Determine the domain where the inverse function is valid, ensuring you respect the domain restriction of h(x)h(x).

I will now work through these calculations and provide the solutions.Here are the results from the calculations:

1. Composition fg(x)f \circ g(x):

  • fg(x)=9(13x6)2+6=xf \circ g(x) = 9\left(-\frac{1}{3} \sqrt{x - 6}\right)^2 + 6 = x.
  • The domain MfgM_{f \circ g} is where g(x)g(x) is valid within the domain of f(x)f(x), which would be x[7,[x \in [7, \infty[.

2. Composition gf(x)g \circ f(x):

  • gf(x)=139x2+66=x2g \circ f(x) = -\frac{1}{3} \sqrt{9x^2 + 6 - 6} = -\sqrt{x^2}.
  • This simplifies to x-|x|, with the domain MgfM_{g \circ f} requiring 9x2+669x^2 + 6 \geq 6, so x[1,]x \in [-1, -\infty].

3. Inverse of h(x)h(x):

  • The inverse of h(x)=x2+285h(x) = \sqrt{x^2 + 28} - 5 is: h1(x)=±(x+5)228h^{-1}(x) = \pm \sqrt{(x + 5)^2 - 28}
  • Given the domain of h(x)h(x) is [0,2][0, 2], we choose the positive branch h1(x)=(x+5)228h^{-1}(x) = \sqrt{(x + 5)^2 - 28}.
  • The domain of the inverse, Mh1M_{h^{-1}}, depends on the range of h(x)h(x), which is the output of h(x)h(x). This leads to x[5,0]x \in [-5, 0].

Would you like further details on any step? Here are 5 related questions:

  1. How do we determine the range of the composite function fgf \circ g?
  2. How does the absolute value affect the result of gfg \circ f?
  3. Why do we select the positive root for the inverse of h(x)h(x)?
  4. Can we visualize these function compositions graphically?
  5. How can we verify the domain restrictions for these compositions?

Tip: When working with composite functions, always ensure the output of one function is valid within the domain of the next function in the composition.

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Math Problem Analysis

Mathematical Concepts

Function Composition
Inverse Functions
Domain and Range

Formulas

f(x) = 9x² + 6
g(x) = -1/3 * √(x - 6)
h(x) = √(x² + 28) - 5

Theorems

Domain restriction in composite functions
Inverse function theorem

Suitable Grade Level

Grade 11-12