Math Problem Statement

If f(x) = 3x-5 and g(f(x)) = 9x^2 -30x - 5, find g(x)

Solution

We are given two functions:

  1. f(x)=3x5f(x) = 3x - 5
  2. g(f(x))=9x230x5g(f(x)) = 9x^2 - 30x - 5

We are tasked with finding g(x)g(x).

Step 1: Express f(x)f(x) in terms of g(x)g(x)

From the problem, we know that g(f(x))=9x230x5g(f(x)) = 9x^2 - 30x - 5. This suggests that gg is a function of the form g(f(x))=g(3x5)g(f(x)) = g(3x - 5).

Step 2: Substitute f(x)=3x5f(x) = 3x - 5 into the equation

Let’s denote y=3x5y = 3x - 5, meaning that g(y)=9x230x5g(y) = 9x^2 - 30x - 5.

Now, we need to express xx in terms of yy. Solve for xx from y=3x5y = 3x - 5:

y=3x5y = 3x - 5 y+5=3xy + 5 = 3x x=y+53x = \frac{y + 5}{3}

Step 3: Rewrite g(y)g(y)

Now, substitute x=y+53x = \frac{y + 5}{3} into the expression for g(f(x))g(f(x)):

g(y)=9(y+53)230(y+53)5g(y) = 9\left( \frac{y + 5}{3} \right)^2 - 30\left( \frac{y + 5}{3} \right) - 5

Step 4: Simplify the expression for g(y)g(y)

First, simplify the square term: (y+53)2=(y+5)29\left( \frac{y + 5}{3} \right)^2 = \frac{(y + 5)^2}{9} Thus: g(y)=9(y+5)2930y+535g(y) = 9 \cdot \frac{(y + 5)^2}{9} - 30 \cdot \frac{y + 5}{3} - 5

Simplifying further: g(y)=(y+5)210(y+5)5g(y) = (y + 5)^2 - 10(y + 5) - 5

Now, expand the terms: g(y)=(y2+10y+25)10(y+5)5g(y) = (y^2 + 10y + 25) - 10(y + 5) - 5 g(y)=y2+10y+2510y505g(y) = y^2 + 10y + 25 - 10y - 50 - 5 g(y)=y230g(y) = y^2 - 30

Thus, the function g(x)g(x) is:

g(x)=x230g(x) = x^2 - 30

Final Answer:

g(x)=x230g(x) = x^2 - 30


Do you want more details on this solution, or do you have any questions?

Here are 5 related questions to expand on this:

  1. How do you verify if two functions are inverses of each other?
  2. Can you find the composition f(g(x))f(g(x)) given f(x)=3x5f(x) = 3x - 5 and g(x)=x230g(x) = x^2 - 30?
  3. What happens to the graph of f(x)f(x) when you compose it with another function?
  4. How do you find the domain and range of g(x)g(x)?
  5. What are the steps to derive the inverse of a function?

Tip: When solving composition problems, carefully track substitutions and ensure to simplify step by step.

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Math Problem Analysis

Mathematical Concepts

Function Composition
Algebra
Quadratic Equations

Formulas

f(x) = 3x - 5
g(f(x)) = 9x^2 - 30x - 5
Quadratic expansion (a+b)^2 = a^2 + 2ab + b^2

Theorems

Substitution of variables
Function decomposition

Suitable Grade Level

Grades 9-11