Graphing f(x)=x^2-x-ln(x) | Summary and Q&A

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August 6, 2018
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blackpenredpen
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Graphing f(x)=x^2-x-ln(x)

TL;DR

This video analyzes the function X^2 - X - Ln(X), discussing its increasing/decreasing intervals, local minimum, concavity, and graph.

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Key Insights

  • #️⃣ The domain of the function is all real numbers greater than zero.
  • 🀘 The increasing and decreasing intervals of the function are determined by analyzing the sign of the first derivative.
  • ☺️ The function has one critical number at X = -1/2 and a local minimum at X = 1.
  • ❓ The second derivative is always positive, indicating that the function is always concave up.
  • πŸ›€ The graph of the function shows increasing and decreasing intervals, a local minimum, and a concave up shape throughout.
  • 🟰 Complex numbers are not considered when solving for solutions of the second derivative equaling zero.

Transcript

okay video we are going to investigate the function X square minus X minus Ln X so we are to the usual business the increasing decreasing local minima local maximum concave up concave down and all the business and then the point of interaction gets not the T already anyway before is turn you see we see that we have an L and X right here that's not ... Read More

Questions & Answers

Q: What is the domain of the function X^2 - X - Ln(X)?

The domain of the function is all real numbers greater than zero because Ln(X) is undefined for X less than or equal to zero.

Q: How are the increasing and decreasing intervals of the function determined?

The increasing and decreasing intervals are found by analyzing the sign of the first derivative. Positive values indicate increasing intervals, while negative values indicate decreasing intervals.

Q: What are the critical numbers of the function X^2 - X - Ln(X)?

The critical number of the function is X = -1/2, found by setting the first derivative equal to zero and solving for X.

Q: Is there a local maximum for the function X^2 - X - Ln(X)?

No, there is no local maximum for this function. Only a local minimum is present at X = 1.

Q: What is the concavity of the function?

The function is always concave up, as the second derivative is always positive.

Q: Can complex numbers be solutions for the second derivative equaling zero?

No, complex numbers are not considered in this case. The second derivative is always positive, so there are no real solutions for it to equal zero.

Q: What is the behavior of the function as X approaches zero and infinity?

As X approaches zero, the function tends towards negative infinity. As X approaches infinity, the function tends towards positive infinity.

Q: How is the graph of the function sketched?

The graph shows an increasing interval from 1 to infinity, a decreasing interval from 0 to 1, a local minimum at X=1, and a concave up shape throughout.

Summary & Key Takeaways

  • The video begins by discussing the domain of the function, which requires X to be greater than zero.

  • The first derivative is calculated to find the increasing and decreasing intervals of the function.

  • The critical numbers are found by setting the first derivative equal to zero, resulting in one critical number, X = -1/2.

  • The function is determined to be increasing from 1 to infinity and decreasing from 0 to 1.

  • The second derivative is then calculated to determine the concavity of the function.

  • The second derivative is always positive, indicating that the function is always concave up.

  • A graph of the function is sketched, showing its increasing and decreasing intervals, local minimum at X = 1, and concave up nature.

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