Defining the Composition of f and g

Oct 13, 2025 by wbrum.org 4 views

In mathematics, the composition of functions is a fundamental concept that allows us to combine two or more functions to create a new function. Given two functions, f(x) and g(x), the composition of f and g, denoted as (f ∘ g)(x) or (g ∘ f)(x), is defined as:

(f ∘ g)(x) = f(g(x))

In this article, we will explore the composition of two given functions, f(x) = 3 - 2x and g(x) = 1/(x + 5), and find the value of (f/g)(8).

Defining the Composition of f and g

To find the composition of f and g, we need to substitute g(x) into f(x). This means we will replace x in f(x) with g(x).

f(g(x)) = 3 - 2g(x)

Now, we substitute g(x) = 1/(x + 5) into the equation:

f(g(x)) = 3 - 2(1/(x + 5))

Simplifying the Composition

To simplify the composition, we need to find a common denominator for the terms in the equation. In this case, the common denominator is (x + 5).

f(g(x)) = 3 - 2/(x + 5)

To simplify further, we can multiply the numerator and denominator of the fraction by (x + 5):

f(g(x)) = 3 - 2(x + 5)/(x + 5)

Now, we can cancel out the (x + 5) terms:

f(g(x)) = 3 - 2

Finding the Value of (f/g)(8)

Now that we have simplified the composition of f and g, we can find the value of (f/g)(8) by substituting x = 8 into the equation:

(f/g)(8) = f(g(8))

We know that g(8) = 1/(8 + 5) = 1/13. Now, we substitute g(8) into f(x):

f(g(8)) = 3 - 2(1/13)

To simplify, we can multiply the numerator and denominator of the fraction by 13:

f(g(8)) = 3 - 2/13

Now, we can find a common denominator for the terms in the equation, which is 13:

f(g(8)) = (39 - 2)/13

Now, we can simplify further:

f(g(8)) = 37/13

Conclusion

In this article, we explored the composition of two given functions, f(x) = 3 - 2x and g(x) = 1/(x + 5), and found the value of (f/g)(8). We simplified the composition of f and g and substituted x = 8 into the equation to find the value of (f/g)(8). The final answer is 37/13, which is approximately 2.846.

Discussion

The composition of functions is a fundamental concept in mathematics that allows us to combine two or more functions to create a new function. In this article, we explored the composition of two given functions, f(x) = 3 - 2x and g(x) = 1/(x + 5), and found the value of (f/g)(8). The final answer is 37/13, which is approximately 2.846.

Answer Key

In the previous article, we explored the composition of two given functions, f(x) = 3 - 2x and g(x) = 1/(x + 5), and found the value of (f/g)(8). In this article, we will answer some frequently asked questions about the composition of functions.

Q: What is the composition of functions?

A: The composition of functions is a way of combining two or more functions to create a new function. Given two functions, f(x) and g(x), the composition of f and g, denoted as (f ∘ g)(x) or (g ∘ f)(x), is defined as:

(f ∘ g)(x) = f(g(x))

Q: How do I find the composition of two functions?

A: To find the composition of two functions, you need to substitute one function into the other. For example, if we want to find the composition of f(x) = 3 - 2x and g(x) = 1/(x + 5), we need to substitute g(x) into f(x):

f(g(x)) = 3 - 2g(x)

Now, we substitute g(x) = 1/(x + 5) into the equation:

f(g(x)) = 3 - 2(1/(x + 5))

Q: What is the difference between (f ∘ g)(x) and (g ∘ f)(x)?

A: The composition of functions is not commutative, meaning that the order of the functions matters. In general, (f ∘ g)(x) ≠ (g ∘ f)(x). For example, if we have f(x) = 3 - 2x and g(x) = 1/(x + 5), then:

(f ∘ g)(x) = f(g(x)) = 3 - 2(1/(x + 5))

(g ∘ f)(x) = g(f(x)) = 1/((3 - 2x) + 5)

As you can see, the two compositions are different.

Q: What are some common applications of the composition of functions?

A: The composition of functions has many applications in mathematics and science. Some common applications include:

Modeling real-world phenomena, such as population growth or chemical reactions
Solving systems of equations
Finding the inverse of a function
Analyzing the behavior of complex systems

Q: How do I evaluate the composition of functions at a specific value?

A: To evaluate the composition of functions at a specific value, you need to substitute the value into the composition. For example, if we want to find the value of (f ∘ g)(8), we need to substitute x = 8 into the composition:

(f ∘ g)(8) = f(g(8))

We know that g(8) = 1/(8 + 5) = 1/13. Now, we substitute g(8) into f(x):

f(g(8)) = 3 - 2(1/13)

To simplify, we can multiply the numerator and denominator of the fraction by 13:

f(g(8)) = 3 - 2/13

Now, we can find a common denominator for the terms in the equation, which is 13:

f(g(8)) = (39 - 2)/13

Now, we can simplify further:

f(g(8)) = 37/13

Conclusion

In this article, we answered some frequently asked questions about the composition of functions. We discussed how to find the composition of two functions, the difference between (f ∘ g)(x) and (g ∘ f)(x), and some common applications of the composition of functions. We also provided examples of how to evaluate the composition of functions at a specific value.

Discussion

The composition of functions is a fundamental concept in mathematics that allows us to combine two or more functions to create a new function. In this article, we explored some common questions and applications of the composition of functions.

Answer Key

Q: What is the composition of functions? A: The composition of functions is a way of combining two or more functions to create a new function.
Q: How do I find the composition of two functions? A: To find the composition of two functions, you need to substitute one function into the other.
Q: What is the difference between (f ∘ g)(x) and (g ∘ f)(x)? A: The composition of functions is not commutative, meaning that the order of the functions matters.
Q: What are some common applications of the composition of functions? A: The composition of functions has many applications in mathematics and science, including modeling real-world phenomena, solving systems of equations, and finding the inverse of a function.
Q: How do I evaluate the composition of functions at a specific value? A: To evaluate the composition of functions at a specific value, you need to substitute the value into the composition.