Math Problem Statement

The functions f and g for x∈ 𝑅 by f(x) = x – 2 and g(x) = ax + b, where a , b ∈ 𝑅. Given that f Β° g(2) = -3 and g Β° 𝑓 (1) = 5, find the value of a and the value of b.

Solution

We are given the following functions:

  • f(x)=xβˆ’2f(x) = x - 2
  • g(x)=ax+bg(x) = ax + b

Also, we know that:

  1. f∘g(2)=βˆ’3f \circ g(2) = -3
  2. g∘f(1)=5g \circ f(1) = 5

We need to find the values of aa and bb. Let's solve this step by step.

Step 1: Use f∘g(2)=βˆ’3f \circ g(2) = -3

This means we first apply gg to 2, and then apply ff to the result of g(2)g(2):

f(g(2))=βˆ’3f(g(2)) = -3

Now, substitute g(x)=ax+bg(x) = ax + b:

g(2)=a(2)+b=2a+bg(2) = a(2) + b = 2a + b

Next, apply ff to g(2)g(2):

f(2a+b)=(2a+b)βˆ’2f(2a + b) = (2a + b) - 2

We are told that f(g(2))=βˆ’3f(g(2)) = -3, so:

(2a+b)βˆ’2=βˆ’3(2a + b) - 2 = -3

Solving this equation:

2a+bβˆ’2=βˆ’32a + b - 2 = -3 2a+b=βˆ’1(Equation 1)2a + b = -1 \quad \text{(Equation 1)}

Step 2: Use g∘f(1)=5g \circ f(1) = 5

This means we first apply ff to 1, and then apply gg to the result of f(1)f(1):

g(f(1))=5g(f(1)) = 5

Now, find f(1)f(1):

f(1)=1βˆ’2=βˆ’1f(1) = 1 - 2 = -1

Next, apply gg to f(1)=βˆ’1f(1) = -1:

g(βˆ’1)=a(βˆ’1)+b=βˆ’a+bg(-1) = a(-1) + b = -a + b

We are told that g(f(1))=5g(f(1)) = 5, so:

βˆ’a+b=5(Equation 2)-a + b = 5 \quad \text{(Equation 2)}

Step 3: Solve the system of equations

We now have the following system of equations:

  1. 2a+b=βˆ’12a + b = -1
  2. βˆ’a+b=5-a + b = 5

Let's solve this system.

From Equation 2, solve for bb:

b=a+5b = a + 5

Substitute this into Equation 1:

2a+(a+5)=βˆ’12a + (a + 5) = -1 3a+5=βˆ’13a + 5 = -1 3a=βˆ’63a = -6 a=βˆ’2a = -2

Now substitute a=βˆ’2a = -2 into the equation b=a+5b = a + 5:

b=βˆ’2+5=3b = -2 + 5 = 3

Final Answer:

  • a=βˆ’2a = -2
  • b=3b = 3

Let me know if you need more details or clarifications!


Here are some related questions for further exploration:

  1. What is the composite function f∘g(x)f \circ g(x)?
  2. How do you solve systems of linear equations algebraically?
  3. What is the importance of composition in function theory?
  4. Can the values of aa and bb be interpreted geometrically?
  5. How would you approach a similar problem where more compositions are involved?

Tip: When solving a system of equations, always try to express one variable in terms of the other to simplify the process.

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Math Problem Analysis

Mathematical Concepts

Algebra
Function Composition
Systems of Linear Equations

Formulas

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

Theorems

Function Composition
Solving Systems of Linear Equations

Suitable Grade Level

Grades 10-12