Math Problem Statement

Find f​(g​(x​)) and g​(f​(x​)) and determine whether the pair of functions f and g are inverses of each other. f​(x​)equals 2 x minus 7     and   g​(x​)equals StartFraction x plus 2 Over 7 EndFraction

Solution

We are given two functions f(x)=2x7f(x) = 2x - 7 and g(x)=x+27g(x) = \frac{x + 2}{7}. To determine if ff and gg are inverses of each other, we need to:

  1. Find f(g(x))f(g(x)).
  2. Find g(f(x))g(f(x)).
  3. Check if f(g(x))=xf(g(x)) = x and g(f(x))=xg(f(x)) = x. If both are true, then ff and gg are inverses.

Step 1: Find f(g(x))f(g(x))

We substitute g(x)=x+27g(x) = \frac{x + 2}{7} into f(x)=2x7f(x) = 2x - 7:

f(g(x))=f(x+27)=2(x+27)7f(g(x)) = f\left(\frac{x + 2}{7}\right) = 2\left(\frac{x + 2}{7}\right) - 7

Simplifying:

f(g(x))=2(x+2)77f(g(x)) = \frac{2(x + 2)}{7} - 7

Now, distribute the 2:

f(g(x))=2x+477f(g(x)) = \frac{2x + 4}{7} - 7

Convert 7 to a fraction with denominator 7:

f(g(x))=2x+47497f(g(x)) = \frac{2x + 4}{7} - \frac{49}{7}

Combine the terms:

f(g(x))=2x+4497=2x457f(g(x)) = \frac{2x + 4 - 49}{7} = \frac{2x - 45}{7}

Thus, f(g(x))=2x457f(g(x)) = \frac{2x - 45}{7}, which is not equal to xx.

Step 2: Find g(f(x))g(f(x))

We substitute f(x)=2x7f(x) = 2x - 7 into g(x)=x+27g(x) = \frac{x + 2}{7}:

g(f(x))=g(2x7)=(2x7)+27g(f(x)) = g(2x - 7) = \frac{(2x - 7) + 2}{7}

Simplifying:

g(f(x))=2x7+27=2x57g(f(x)) = \frac{2x - 7 + 2}{7} = \frac{2x - 5}{7}

Thus, g(f(x))=2x57g(f(x)) = \frac{2x - 5}{7}, which is not equal to xx.

Conclusion:

Since neither f(g(x))=xf(g(x)) = x nor g(f(x))=xg(f(x)) = x, the functions f(x)=2x7f(x) = 2x - 7 and g(x)=x+27g(x) = \frac{x + 2}{7} are not inverses of each other.


Do you need more details or have any questions?

Here are 5 related questions to expand your understanding:

  1. How can you tell if two functions are inverses using their compositions?
  2. What would the function inverse of f(x)=2x7f(x) = 2x - 7 look like?
  3. Why is the condition f(g(x))=xf(g(x)) = x important for determining inverses?
  4. Can two functions be partially inverse (e.g., for some but not all values)?
  5. How do graphical methods help in identifying inverse functions?

Tip: When composing functions, carefully apply each function's rule and simplify step by step to avoid errors in the process.

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Math Problem Analysis

Mathematical Concepts

Algebra
Function Composition
Inverse Functions

Formulas

f(x) = 2x - 7
g(x) = (x + 2) / 7
f(g(x)) and g(f(x))

Theorems

Inverse Function Theorem

Suitable Grade Level

Grades 9-11