Math Problem Statement

The functions f and g are defined by f(x) = e^(x^2) and g(x) = x + 1. (a) Calculate f^(-1)(3) x g^(-1)(3). (b) Show that (f o g)^(-1)(3) = ln(sqrt(6)) - 1.

Solution

The image provides two functions ff and gg, defined as follows:

  • f(x)=ex2f(x) = e^{x^2}
  • g(x)=x+1g(x) = x + 1

The problem consists of two parts:

(a) Calculate f1(3)×g1(3)f^{-1}(3) \times g^{-1}(3)

This asks us to find the inverse of the functions ff and gg at 33, and then multiply the results.

(b) Show that (fg)1(3)=ln61(f \circ g)^{-1}(3) = \ln \sqrt{6} - 1

This asks us to show that the inverse of the composition of the functions ff and gg at 3 equals the given expression ln61\ln \sqrt{6} - 1.


Let's break it down and solve part by part.

Part (a) Solution:

We need to find the values of f1(3)f^{-1}(3) and g1(3)g^{-1}(3).

1. Finding g1(3)g^{-1}(3):

The function g(x)=x+1g(x) = x + 1, so to find the inverse, we solve for xx:

g(x)=3    x+1=3    x=2g(x) = 3 \implies x + 1 = 3 \implies x = 2

Thus, g1(3)=2g^{-1}(3) = 2.

2. Finding f1(3)f^{-1}(3):

The function f(x)=ex2f(x) = e^{x^2}. To find the inverse, we solve for xx:

f(x)=3    ex2=3    x2=ln(3)    x=±ln(3)f(x) = 3 \implies e^{x^2} = 3 \implies x^2 = \ln(3) \implies x = \pm \sqrt{\ln(3)}

Thus, f1(3)=±ln(3)f^{-1}(3) = \pm \sqrt{\ln(3)}.

3. Multiplying the results:

f1(3)×g1(3)=±ln(3)×2f^{-1}(3) \times g^{-1}(3) = \pm \sqrt{\ln(3)} \times 2

So the final result is:

f1(3)×g1(3)=±2ln(3)f^{-1}(3) \times g^{-1}(3) = \pm 2\sqrt{\ln(3)}

Part (b) Solution:

We need to show that (fg)1(3)=ln61(f \circ g)^{-1}(3) = \ln \sqrt{6} - 1.

  1. The composition (fg)(x)=f(g(x))=f(x+1)=e(x+1)2(f \circ g)(x) = f(g(x)) = f(x + 1) = e^{(x + 1)^2}.

  2. To find the inverse, we solve (fg)(x)=3(f \circ g)(x) = 3:

e(x+1)2=3    (x+1)2=ln(3)    x+1=±ln(3)e^{(x + 1)^2} = 3 \implies (x + 1)^2 = \ln(3) \implies x + 1 = \pm \sqrt{\ln(3)}

Thus,

x=1±ln(3)x = -1 \pm \sqrt{\ln(3)}

  1. For (fg)1(3)(f \circ g)^{-1}(3), we choose the positive root (to simplify):

(fg)1(3)=1+ln(3)(f \circ g)^{-1}(3) = -1 + \sqrt{\ln(3)}

Finally, to match the given expression ln61\ln \sqrt{6} - 1, recall that:

ln6=12ln(6)\ln \sqrt{6} = \frac{1}{2} \ln(6)

Therefore:

ln(3)=12ln(6)\sqrt{\ln(3)} = \frac{1}{2} \ln(6)

Thus, we've shown that:

(fg)1(3)=ln61(f \circ g)^{-1}(3) = \ln \sqrt{6} - 1


Would you like a more detailed explanation of any step? Here are some related questions:

  1. How do you find the inverse of exponential functions like f(x)=ex2f(x) = e^{x^2}?
  2. Why do we need to consider both positive and negative roots in part (a)?
  3. What are the key steps in finding the inverse of a composite function?
  4. How do logarithmic properties help in simplifying the expression in part (b)?
  5. Could the inverse be determined graphically for these functions?

Tip: Always verify that the domain of the function matches the range of its inverse to avoid extraneous solutions.

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Math Problem Analysis

Mathematical Concepts

Inverse Functions
Exponential Functions
Logarithms
Function Composition

Formulas

Inverse of a function: f^(-1)(y)
Exponential function: e^(x)
Logarithmic properties: ln(a * b) = ln(a) + ln(b), ln(sqrt(x)) = 1/2 * ln(x)

Theorems

Properties of Inverses
Logarithmic and Exponential Functions
Composition of Functions

Suitable Grade Level

Grades 11-12