Math Problem Statement

Find the domain of the composition function (f ∘ g)(x) = f(g(x)) where f(x) = √(3 - x) and g(x) = 2/(x + 1).

Solution

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Problem:

It is given that f(x)=3xf(x) = \sqrt{3 - x} and g(x)=2x+1g(x) = \frac{2}{x + 1}. We need to find the domain of the composition function (fg)(x)=f(g(x))(f \circ g)(x) = f(g(x)).

Step-by-step Solution:

  1. Domain of f(x)=3xf(x) = \sqrt{3 - x}:

    For the square root function to be defined, the expression inside the square root must be non-negative:

    3x03 - x \geq 0

    Solving for xx:

    x3x \leq 3

    Thus, the domain of f(x)f(x) is (,3](-\infty, 3].

  2. Domain of g(x)=2x+1g(x) = \frac{2}{x + 1}:

    For the fraction to be defined, the denominator must not be zero:

    x+10    x1x + 1 \neq 0 \implies x \neq -1

    Thus, the domain of g(x)g(x) is (,1)(1,)(-\infty, -1) \cup (-1, \infty).

  3. Domain of the composition function (fg)(x)=f(g(x))(f \circ g)(x) = f(g(x)):

    To find the domain of the composition, we need to determine the set of all xx values that are in the domain of g(x)g(x) such that g(x)g(x) is in the domain of f(x)f(x).

    Since f(x)=3xf(x) = \sqrt{3 - x}, we need:

    3g(x)0.3 - g(x) \geq 0.

    Substituting g(x)=2x+1g(x) = \frac{2}{x + 1}:

    32x+10.3 - \frac{2}{x + 1} \geq 0.

    Rearranging this inequality:

    3(x+1)20,3(x + 1) - 2 \geq 0,

    3x+320,3x + 3 - 2 \geq 0,

    3x+10,3x + 1 \geq 0,

    x13.x \geq -\frac{1}{3}.

  4. Combine the domain conditions:

    We also know that x1x \neq -1. Combining the conditions x13x \geq -\frac{1}{3} and x1x \neq -1, we get the domain:

    x[13,){1}.x \in \left[-\frac{1}{3}, \infty\right) \setminus \{-1\}.

Conclusion:

The domain of the function (fg)(x)(f \circ g)(x) is:

[13,){1}.\left[-\frac{1}{3}, \infty\right) \setminus \{-1\}.

Would you like more details on any specific step or do you have any questions?

Follow-up Questions:

  1. What is the range of the composition function (fg)(x)(f \circ g)(x)?
  2. How would you find the domain of (gf)(x)(g \circ f)(x) instead?
  3. Can you explain why the composition of two functions depends on the range of the inner function?
  4. What happens to the domain if both functions f(x)f(x) and g(x)g(x) are modified?
  5. How would you graph the composition function (fg)(x)(f \circ g)(x)?

Tip:

Always carefully consider the domains of

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Math Problem Analysis

Mathematical Concepts

Functions
Composition of Functions
Domain and Range
Inequalities

Formulas

Domain of √(3 - x): 3 - x ≥ 0
Domain of 2/(x + 1): x ≠ -1

Theorems

Domain restrictions for square root functions
Domain restrictions for rational functions

Suitable Grade Level

Grades 10-12