What Are Limits and Derivatives and How Do You Solve Them?

  • Thread starter Thread starter MercuryRising
  • Start date Start date
  • Tags Tags
    Derivatives Limits
Click For Summary

Homework Help Overview

The discussion revolves around limits and derivatives, specifically addressing the limit of a trigonometric expression as x approaches zero and the equation of a tangent line to a given function. Participants are seeking clarification and assistance with these calculus concepts.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the limit of sin2x/sin5x and consider transforming it into a more manageable form. Questions arise about the application of L'Hopital's rule and the conditions for using it. The tangent line problem prompts discussions about finding the correct slope and point of tangency.

Discussion Status

There is an active exploration of different methods to approach the limit problem, with some participants suggesting transformations and questioning assumptions. The tangent line discussion includes considerations of how to find the slope and the appropriate point on the curve.

Contextual Notes

Participants note the indeterminate form encountered in the limit problem and the need for careful application of rules and definitions related to derivatives and tangent lines. There is also a mention of the original post being miscategorized, which may affect the visibility of responses.

MercuryRising
Messages
28
Reaction score
0
i have a test tomorrow but i have no idea how to do these probelms...
1) lim x->0 sin2x/sin5x

2) write an equation for the stright line through (1,0) that is tangent to the graph of y= x + 1/x...

thanks in advance
 
Physics news on Phys.org
Is there a reason for posting this under "differential equations"?? I'm going to move it to "Homework, k-12". I think it will get a better response there.

1) What if this were [itex]lim_{y,z->0}\frac{sin y}{y}\frac{z}{sin z}[/itex]? Could you do it then? Can you think of a way to change it into that form?

2) One definition of "derivative" is that it is the "slope of the tangent line". Would knowing the slope of the line help?
 
sorry, i was in a rush so i posted it in the wrong section :biggrin:
1) i tried (2x/2x) (sin2x)/sin(5x) -> (2x/sin5x) (sin2x)(2x)..now i don't know how to get rid of the (2x/sin5x)

2) hmm...the derivative i got was (X^2-1)/x^2. do i just plug in a random number to get a slope then use point sliope formula to make it include (1,0)?
 
1) Note that you have the indeterminate form 0/0. Does this suggest anybody's Rule?

2) You don't use a random point. You have to find a point (x, y) such that the slope of the line (which is constant, of course) equals the slope of the curve at that point. Note that the line will also pass through that point. Think simultaneous equations.
 
L'Hopital's rule will work (easily) but I would consider it overkill! You wouldn't want to do this the easy way, would you?

MercuryRising: You changed [tex]\frac{sin 2x}{sin 5x}[/tex] to [tex]\frac{sin 2x}{2x}\frac{5x}{sin 5x}[/tex] by multiplying the numerator by 5x and denominator by 2x. Of course you can't do that! But you can multiply both numerator and denominator by the same thing. That gives [tex]\frac{sin 2x}{2x}\frac{5x}{sin 5x}\frac{2x}{5x}[/tex]. Can you find the limit of that?
 
HallsofIvy said:
L'Hopital's rule will work (easily) but I would consider it overkill! You wouldn't want to do this the easy way, would you?

As a matter of fact, yes. :smile:
 
Diane_ said:
Does this suggest anybody's Rule?

Maybe L'Anybody's Rule would habe been a better hint. :smile:
 
Do you have a cold, Tom?
 
No, I do not habe a cold. :-p
 

Similar threads

Replies
8
Views
2K
  • · Replies 20 ·
Replies
20
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 10 ·
Replies
10
Views
1K
  • · Replies 1 ·
Replies
1
Views
1K
Replies
13
Views
2K
Replies
4
Views
2K
  • · Replies 8 ·
Replies
8
Views
4K
  • · Replies 21 ·
Replies
21
Views
1K
  • · Replies 53 ·
2
Replies
53
Views
7K