Math Problem Statement

Evaluate the function for values of x that approach 1 from the left and from the right.

f(x) = 

9

x3 − 1   lim x→1− f(x) =      

lim x→1+ f(x) =

Solution

Let's evaluate the function f(x)=9x31f(x) = \frac{9}{x^3 - 1} as xx approaches 1 from the left (denoted as x1x \to 1^-) and from the right (denoted as x1+x \to 1^+).

1. Understanding the function:

The function is given by:

f(x)=9x31f(x) = \frac{9}{x^3 - 1}

The expression x31x^3 - 1 can be factored using the difference of cubes:

x31=(x1)(x2+x+1)x^3 - 1 = (x - 1)(x^2 + x + 1)

Thus, the function can be rewritten as:

f(x)=9(x1)(x2+x+1)f(x) = \frac{9}{(x - 1)(x^2 + x + 1)}

2. Evaluating the limit as x1x \to 1^-:

As xx approaches 1 from the left (values slightly less than 1), the factor (x1)(x - 1) is slightly negative. The factor (x2+x+1)(x^2 + x + 1) is always positive for real xx.

So, as xx approaches 1 from the left:

  • (x1)(x - 1) approaches 0 from the negative side.
  • (x2+x+1)(x^2 + x + 1) approaches 3 (since 12+1+1=31^2 + 1 + 1 = 3).

This makes the function:

f(x)9(a small negative number)×3f(x) \approx \frac{9}{\text{(a small negative number)} \times 3} \approx -\infty

So,

limx1f(x)=\lim_{x \to 1^-} f(x) = -\infty

3. Evaluating the limit as x1+x \to 1^+:

As xx approaches 1 from the right (values slightly greater than 1), the factor (x1)(x - 1) is slightly positive. The factor (x2+x+1)(x^2 + x + 1) is again always positive.

So, as xx approaches 1 from the right:

  • (x1)(x - 1) approaches 0 from the positive side.
  • (x2+x+1)(x^2 + x + 1) approaches 3.

This makes the function:

f(x)9(a small positive number)×3+f(x) \approx \frac{9}{\text{(a small positive number)} \times 3} \approx +\infty

So,

limx1+f(x)=+\lim_{x \to 1^+} f(x) = +\infty

Final Answer:

  • limx1f(x)=\lim_{x \to 1^-} f(x) = -\infty
  • limx1+f(x)=+\lim_{x \to 1^+} f(x) = +\infty

These results indicate that the function has a vertical asymptote at x=1x = 1, where the function behavior is sharply different on either side of the asymptote.

Would you like to explore these limits further, or do you have any additional questions?


Here are 5 related questions for further exploration:

  1. How would the function behave as xx approaches 1 from values far from 1?
  2. Can you find the limit of f(x)f(x) as xx approaches 0 or infinity?
  3. What happens to the function if you change the exponent in the denominator from 3 to 2?
  4. How would the limit change if the function were 9x3+1\frac{9}{x^3 + 1} instead?
  5. Can you plot the graph of this function to visually confirm the asymptotic behavior?

Tip: When dealing with limits involving asymptotes, always consider the sign and magnitude of the components in the function as they approach critical values.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Limits
Asymptotes
Rational Functions

Formulas

Limit definition
Factoring

Theorems

-

Suitable Grade Level

Grades 11-12