Math Problem Statement

If f(x) = 2 ^ log_3(x) , then the value of f ^ - 1 * (16) will be? (a) 27 (b) 1/27 (c) 81 (d) 1/81

Solution

To solve for f1(16)f^{-1}(16), we need to first understand the function f(x)=2log3(x)f(x) = 2^{\log_3(x)}.

Step 1: Find f(x)f(x) in a simpler form

We know: f(x)=2log3(x)f(x) = 2^{\log_3(x)}

To understand this function, let's rewrite the logarithm using a change of base formula. The change of base formula states:

log3(x)=log2(x)log2(3)\log_3(x) = \frac{\log_2(x)}{\log_2(3)}

Substituting this into the expression for f(x)f(x):

f(x)=2log3(x)=2log2(x)log2(3)f(x) = 2^{\log_3(x)} = 2^{\frac{\log_2(x)}{\log_2(3)}}

Now, using the exponent rule abc=(ab)ca^{b \cdot c} = (a^b)^c, we can rewrite f(x)f(x):

f(x)=(2log2(x))1log2(3)f(x) = \left( 2^{\log_2(x)} \right)^{\frac{1}{\log_2(3)}}

Since 2log2(x)=x2^{\log_2(x)} = x, we get:

f(x)=x1log2(3)f(x) = x^{\frac{1}{\log_2(3)}}

Step 2: Find f1(x)f^{-1}(x)

To find f1(x)f^{-1}(x), we express xx as a function of yy:

y=x1log2(3)y = x^{\frac{1}{\log_2(3)}}

Now, solving for xx gives:

y=x1log2(3)y = x^{\frac{1}{\log_2(3)}} ylog2(3)=xy^{\log_2(3)} = x

So, f1(y)=ylog2(3)f^{-1}(y) = y^{\log_2(3)}.

Step 3: Evaluate f1(16)f^{-1}(16)

Now, we substitute y=16y = 16 into f1(y)f^{-1}(y):

f1(16)=16log2(3)f^{-1}(16) = 16^{\log_2(3)}

Since 16=2416 = 2^4:

f1(16)=(24)log2(3)f^{-1}(16) = (2^4)^{\log_2(3)} =24log2(3)= 2^{4 \cdot \log_2(3)} =2log2(34)= 2^{\log_2(3^4)} =34= 3^4 =81= 81

Therefore, the value of f1(16)f^{-1}(16) is 81\boxed{81}.

Answer:

(c) 81

Would you like more details, or do you have any questions?

Here are five related questions to expand on this topic:

  1. What is the domain and range of the function f(x)=2log3(x)f(x) = 2^{\log_3(x)}?
  2. How would you find the inverse of a logarithmic function in general?
  3. Can you express f(x)=2log3(x)f(x) = 2^{\log_3(x)} using natural logarithms?
  4. What is the graphical interpretation of finding the inverse of a function?
  5. How would you solve for f1(32)f^{-1}(32) if f(x)=2log3(x)f(x) = 2^{\log_3(x)}?

Tip: Understanding the change of base formula for logarithms can simplify many calculations and is a valuable tool when dealing with functions involving different bases.

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Math Problem Analysis

Mathematical Concepts

Exponential Functions
Logarithms
Inverse Functions

Formulas

Change of base formula
Exponentiation rules

Theorems

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Suitable Grade Level

High School