How Can I Solve a Question on Directional Derivatives Without Knowing the Point?

  • Thread starter Thread starter SANGHERA.JAS
  • Start date Start date
  • Tags Tags
    Derivatives
Click For Summary
SUMMARY

The discussion centers on the challenge of calculating directional derivatives without a specified point. Participants clarify that while a unit vector can be derived from an angle, the absence of a specific point makes it impossible to compute the directional derivative accurately. The consensus is that the problem requires additional information to yield a definitive answer, as exemplified by the textbook's answer of -(1/2), which implies a specific point is necessary for calculation.

PREREQUISITES
  • Understanding of directional derivatives in multivariable calculus
  • Familiarity with unit vectors and their calculation
  • Knowledge of the gradient vector and its role in directional derivatives
  • Basic concepts of limits and continuity in calculus
NEXT STEPS
  • Study the concept of directional derivatives in multivariable calculus
  • Learn how to compute unit vectors from angles
  • Explore the significance of the gradient vector in finding directional derivatives
  • Review problems involving directional derivatives with specified points for practice
USEFUL FOR

Students and educators in calculus, particularly those focusing on multivariable calculus and directional derivatives, as well as anyone preparing for examinations involving these concepts.

SANGHERA.JAS
Messages
50
Reaction score
0
According to the statement(attached file) in order to find the directional derivative I must know unit vector along the direction and the point at which to find the directional derivatives. From the angle I can find out the direction (as the cosine of the angle) but not the point. Then how can I solve this question?


Your help is much appreciated.
 

Attachments

Physics news on Phys.org
The problem wants you to find the directional derivative at all points. It's like asking you what g'(x) is as opposed to g'(1). Does that make sense?
 
vela said:
The problem wants you to find the directional derivative at all points. It's like asking you what g'(x) is as opposed to g'(1). Does that make sense?

But the answer according to my textbook is -(1/2). Thus there should be a point.
 
Yes, you're right. You can't solve the problem to get that answer without additional information.
 
But this question was put in examination. So it must have answer
 
Question: A clock's minute hand has length 4 and its hour hand has length 3. What is the distance between the tips at the moment when it is increasing most rapidly?(Putnam Exam Question) Answer: Making assumption that both the hands moves at constant angular velocities, the answer is ## \sqrt{7} .## But don't you think this assumption is somewhat doubtful and wrong?

Similar threads

Replies
9
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
Replies
22
Views
3K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 4 ·
Replies
4
Views
3K
Replies
7
Views
2K
  • · Replies 4 ·
Replies
4
Views
1K
  • · Replies 8 ·
Replies
8
Views
1K