Find dy/dx, which way should I use?

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SUMMARY

The discussion focuses on finding the derivative dy/dx for the equation Y^x = X^y using logarithmic differentiation. Participants emphasize the importance of differentiating equivalent forms of the equation, specifically using natural logarithms to simplify the process. The correct differentiation technique involves applying the properties of logarithms, such as Ln(Y^x) = Ln(X^y), leading to the equation X • Ln(y) = Y • Ln(x). Participants clarify the distinction between "differentiate" and "derive," asserting that improper terminology can lead to confusion.

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Homework Statement

.[/B]
Find dy/dx
Y^x = X^y

Homework Equations


F'( Ln(x)) = 1/x
Lnx^y = yLnx

The Attempt at a Solution


Ln(Y^x) = Ln(X^y)
X • Lny = Y • Lnx , should I differentiate now or :
Y = X • Lny/Lnx
Y = X • Logxy , then differentiate ?
 
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It does not matter when you differentiate as long as the equality you are differentiating is equivalent to the original one.
 
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Mamdoh Abughalion said:

Homework Statement

.[/B]
Find dy/dx
Y^x = X^y

Homework Equations


F'( Ln(x)) = 1/x
Lnx^y = yLnx

The Attempt at a Solution


Ln(Y^x) = Ln(X^y)
X • Lny = Y • Lnx , should I derive now or :
Y = X • Lny/Lnx
Y = X • Logxy , then derive?
To find a derivative, you differentiate. The word derive means something else.
 
Orodruin said:
It does not matter when you differentiate as long as the equality you are differentiating is equivalent to the original one.
I know that , but my instructer told me that the second way is too much " dangerous " and may lead to wrong solution .
 
Also, please don't write ##F'(\ln x) = \frac 1 x##. There is no ##F##. What you mean, and should write, is ##(\ln x)' = \frac 1 x## when you want to give a derivative formula.
 
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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?

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