Polar Coordinates: Find dy/dx Problem Solution

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SUMMARY

The forum discussion focuses on solving the derivative dy/dx in polar coordinates, specifically addressing the equation dy/dx = -cos(θ)sin(θ) + (1-sin(θ))cos(θ)/-cos²(θ) - (1-sin(θ))sin(θ). Participants clarify that the solution does not involve trigonometric identities but rather algebraic manipulation. The confusion arises from the representation of the answer, which can be expressed as -cos(θ)sin(θ) + rcos(θ) for clarity. The discussion emphasizes the importance of viewing the problem through an algebraic lens rather than a purely trigonometric one.

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  • Familiarity with basic trigonometric identities
  • Knowledge of algebraic manipulation techniques
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Students studying calculus, particularly those working with polar coordinates, as well as educators seeking to clarify concepts related to derivatives in non-Cartesian systems.

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Homework Statement



Find dy/dx
Problem in picture below

Homework Equations


The Attempt at a Solution


[PLAIN]http://img28.imageshack.us/img28/7162/76013837.png

The answer for this is
dy/dx = -cos\theta sin\theta + (1-sin\theta)cos\theta/-cos^2\theta - (1-sin/theta)sin\theta I cannot figure out why I'm not getting the same or equivalent for dy/dtheta... and trig makes me woozy.
 
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Your dy/d\theta is equivalent. Take a look at the second to last line of your calculation before you used the double angle equation.
 
I did Peng Peng, but I just can't see it -_- Which type of identity did they use?
 
They didn't! \cos(\theta) - 2\sin(\theta)\cos(\theta) = -\cos(\theta)\sin(\theta) +(1-\sin(\theta))\cos(\theta)

The tex translator seems to be pooping itself.
 
@_@ I really need to take another trig class...let me try to work it out.
 
Just write out the right hand side. There is no trig involved. They just wrote down the answer in a way that the 'r' shows up again. They could have written it

-\cos(\theta)\sin(\theta) +r\cos(\theta)

if they wanted to be more explicit.
 
omg I see it now...maybe I need to take another algebra class -_-

Thx peng!
 
Pengwuino said:
Just write out the right hand side. There is no trig involved. They just wrote down the answer in a way that the 'r' shows up again. They could have written it

-\cos(\theta)\sin(\theta) +r\cos(\theta)

if they wanted to be more explicit.

yes thanks peng I saw it after I started to think "algebra" and not trig -_-
 

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