How Does the Derivative of sin(x) Equal cos(x)?

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SUMMARY

The derivative of the sine function, defined as y = sin(x), is proven to be y' = cos(x) using the limit definition of a derivative. The limit definition is expressed as f'(x) = lim(h→0) (f(x+h) - f(x)) / h. Understanding limits is crucial for grasping this concept, as it forms the foundation for calculating derivatives. The discussion emphasizes the importance of mastering limits before attempting to prove derivatives, particularly for trigonometric functions.

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  • Understanding of limits in calculus
  • Familiarity with the definition of a derivative
  • Basic knowledge of trigonometric functions
  • Experience with the squeeze theorem
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  • Study the concept of limits in calculus
  • Learn the formal definition of a derivative
  • Explore the squeeze theorem and its applications
  • Practice proving derivatives of other trigonometric functions
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Students learning calculus, particularly those struggling with derivatives and limits, as well as educators seeking to clarify these concepts for their students.

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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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What is the definition of the derivative?
 
?? 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
 
.. ?
woahw.. so... how do i apply that
to the sin graph?..
: no clue..
maybe i'll go over it again..
 
You set f(x)=sin(x) in the expression f'(x)=\lim_{h\to0}\;\frac{f(x+h)-f(x)}{h}Hint: if you actually read through that thread, then you may be surprised as to what you find...[/color][/size]

I'm moving this to calc&beyond, since it is calculus!
 
.. 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?..
 
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.
 
^^ 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:
 

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