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If [tex]f(x)=x^2-1[/tex] and [tex]g(x)=2x-3[/tex], what is the domain of [tex](f \circ g)(x)[/tex]?

A. [tex](-\infty, \infty)[/tex]
B. [tex][-1, \infty)[/tex]
C. [tex][-5, \infty)[/tex]
D. [tex](\infty, -\infty)[/tex]


Sagot :

Let's determine the domain of the composite function [tex]\((f \circ g)(x)\)[/tex], which is defined as [tex]\(f(g(x))\)[/tex].

### Step-by-Step Solution:

1. Understand the individual functions:
- Function [tex]\(f(x)\)[/tex] is defined as [tex]\(f(x) = x^2 - 1\)[/tex].
- Function [tex]\(g(x)\)[/tex] is defined as [tex]\(g(x) = 2x - 3\)[/tex].

2. Determine the domain of [tex]\(g(x)\)[/tex]:
- [tex]\(g(x) = 2x - 3\)[/tex] is a linear function.
- Linear functions are defined for all real numbers.
- Hence, the domain of [tex]\(g(x)\)[/tex] is [tex]\((-\infty, \infty)\)[/tex].

3. Determine the domain of [tex]\(f(x)\)[/tex]:
- [tex]\(f(x) = x^2 - 1\)[/tex] is a polynomial function.
- Polynomial functions are also defined for all real numbers.
- Thus, the domain of [tex]\(f(x)\)[/tex] is [tex]\((-\infty, \infty)\)[/tex].

4. Composite function [tex]\(f(g(x))\)[/tex]:
- The domain of the composite function [tex]\(f(g(x))\)[/tex] is determined by the domain of [tex]\(g(x)\)[/tex] first and then the domain of [tex]\(f(x)\)[/tex] applied to [tex]\(g(x)\)[/tex].

5. Apply the domains:
- Since both [tex]\(g(x)\)[/tex] and [tex]\(f(x)\)[/tex] are defined for all real numbers, the composite function [tex]\(f(g(x))\)[/tex] will also be defined for all real numbers.

6. Conclusion:
- The domain of [tex]\((f \circ g)(x)\)[/tex] is [tex]\((-\infty, \infty)\)[/tex].

Therefore, the domain of [tex]\((f \circ g)(x)\)[/tex] is [tex]\((-\infty, \infty)\)[/tex]. The correct answer is:
[tex]\[ \boxed{(-\infty, \infty)} \][/tex]