Math Problem Statement

if f(x)=sqrt:x and g(x)= -3x-2, find (fog)(x) and (gof)(x)

Solution

Given the functions:

  • f(x)=xf(x) = \sqrt{x}
  • g(x)=3x2g(x) = -3x - 2

We need to find both:

  1. (fg)(x)=f(g(x))(f \circ g)(x) = f(g(x))
  2. (gf)(x)=g(f(x))(g \circ f)(x) = g(f(x))

1. Finding (fg)(x)=f(g(x))(f \circ g)(x) = f(g(x))

Substitute g(x)g(x) into f(x)f(x):

(fg)(x)=f(g(x))=f(3x2)(f \circ g)(x) = f(g(x)) = f(-3x - 2) Now, apply f(x)=xf(x) = \sqrt{x} to the expression:

(fg)(x)=3x2(f \circ g)(x) = \sqrt{-3x - 2}

So, (fg)(x)=3x2(f \circ g)(x) = \sqrt{-3x - 2}

2. Finding (gf)(x)=g(f(x))(g \circ f)(x) = g(f(x))

Substitute f(x)f(x) into g(x)g(x):

(gf)(x)=g(f(x))=g(x)(g \circ f)(x) = g(f(x)) = g(\sqrt{x}) Now, apply g(x)=3x2g(x) = -3x - 2 to x\sqrt{x}:

(gf)(x)=3x2(g \circ f)(x) = -3\sqrt{x} - 2

Thus, (gf)(x)=3x2(g \circ f)(x) = -3\sqrt{x} - 2

Final Answer:

  • (fg)(x)=3x2(f \circ g)(x) = \sqrt{-3x - 2}
  • (gf)(x)=3x2(g \circ f)(x) = -3\sqrt{x} - 2

Would you like more details or have any questions about these functions?

Here are five related questions to deepen understanding:

  1. How do you compute the domain of (fg)(x)(f \circ g)(x)?
  2. What is the domain of (gf)(x)(g \circ f)(x)?
  3. Can the composition (fg)(x)(f \circ g)(x) ever be negative?
  4. What is the range of (fg)(x)(f \circ g)(x) for specific values of xx?
  5. How does the behavior of these compositions change as xx \to \infty?

Tip: Always verify the domain of composite functions to ensure that the operations are valid at each stage.

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Math Problem Analysis

Mathematical Concepts

Function Composition
Square Roots
Linear Functions

Formulas

(f ∘ g)(x) = f(g(x))
(g ∘ f)(x) = g(f(x))

Theorems

Function Composition Rule
Domain and Range of Composite Functions

Suitable Grade Level

Grades 9-12