Prove Derivatives: Help Needed!

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In summary, the conversation was about proving the derivative of y=sinx using the definition of a derivative. One person was struggling with understanding the concept and asked for help, while another provided a thread from the learning materials forum as a resource. The conversation also touched on the importance of understanding limits and the squeeze theorem in order to successfully prove the derivative.
  • #1
Wholewheat458
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Homework Statement


Prove using the definition of a derivative.
If y=sinx, then y1=cosx


Homework Equations


.. ? identities maybe..? i don't really know much about derivatives..


The Attempt at a Solution


y = sinx..
y1 = (1)sinx^1-1
y1 = 1..
how is that suppose to equal cosx?? !
i haven't got a clue, any help would really be appreciated!
:shy:
 
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  • #2
What is the definition of the derivative?
 
  • #3
?? I'm not all that certain..
its got somethink to do with graphs, but..
idk, i been looking at a graph of y = sinx
but i don't know what to do with it: oy
 
  • #5
.. ?
woahw.. so... how do i apply that
to the sin graph?..
: no clue..
maybe i'll go over it again..
 
  • #6
You set f(x)=sin(x) in the expression [tex] f'(x)=\lim_{h\to0}\;\frac{f(x+h)-f(x)}{h}[/tex]Hint: if you actually read through that thread, then you may be surprised as to what you find...

I'm moving this to calc&beyond, since it is calculus!
 
  • #7
.. i don't think i understand the formula..
: f(x) = sinx .. then.
= sinx = lim(h-->) sin(x+h) - sinx/ h
... this is so wrong
wait, what is h?..
 
  • #8
Have you studied limits before? From your posts here, it sounds like you haven't. This problem will be incredibly difficult if you have not heard about limits before, and I can't see why it would have been set for you to try.
 
  • #9
^^ i don't know why either!
ahhahaa! i think i'll just skip it for now..
thanks for your help
 
  • #10
Try learning limits, then the definition of derivative, then the squeeze theorem and then you should be able to make a fairly decent proof of it.
 
  • #11
Wholewheat458 said:
^^ i don't know why either!
ahhahaa! i think i'll just skip it for now..
thanks for your help

Skipping is not possible if you are learning about derivatives right now.
This will haunt you later :blushing:
 

1. What is a derivative?

A derivative is a mathematical concept that represents the rate of change of a function with respect to its independent variable. It measures the slope of a curve at a specific point and indicates how much a function is changing at that point.

2. Why is it important to prove derivatives?

Proving derivatives is important because it provides a rigorous and formal way to verify the accuracy of a function's rate of change. This is crucial in fields such as physics and engineering where precise measurements and calculations are necessary.

3. How do you prove a derivative?

The most common method for proving a derivative is using the limit definition, which involves finding the limit of the difference quotient as the change in the independent variable approaches zero. Other methods include using derivative rules and properties, and using the concept of continuity.

4. What is the role of derivatives in real-world applications?

Derivatives have a wide range of applications in various fields such as physics, economics, and engineering. They are used to model and analyze rates of change, optimize functions, and solve problems involving motion, growth, and decay.

5. Are there any common mistakes to avoid when proving derivatives?

One common mistake when proving derivatives is assuming that a function is differentiable at a point without verifying it. It is important to check for continuity and differentiability before applying derivative rules or using the limit definition. Another mistake is not simplifying the expression before taking the limit, which can lead to incorrect results.

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