What is the derivative for x^2 + y^2 + ln(2) = xy?

  • Thread starter antinerd
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    Derivative
In summary, the homework statement is to find dy/dx in terms of x and y. The Attempt at a Solution is to try and find the answer to the equation x+y=1. The correct derivative for xy is the product rule, and implicit differentiation is needed to apply it. The final equation is x+y=1.
  • #36
That is correct. Now solve for dy/dx.
 
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  • #37
Dick said:
That is correct. Now solve for dy/dx.

That's where I need the help... :(

Is it now just algebraic manipulation, or do I have to do something with the terms:

2y (dy/dx) and x (dy/dx)

?
 
  • #38
It is just algebraic manipulation. The calculus is over. Move both terms to one side of the equation and factor out dy/dx.
 
  • #39
You're the man, Dick!

Thanks to everyone.

Final answer:

dy/dx = (-x+1) / y

PLEASE TELL ME THIS IS CORRECT! THEN I CAN BLOW THROUGH THE REST OF 'EM!
 
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  • #40
antinerd said:
You're the man, Dick!

Thanks to everyone.

Final answer:

dy/dx = (-x+1) / y

PLEASE TELL ME THIS IS CORRECT! THEN I CAN BLOW THROUGH THE REST OF 'EM!

I'm getting dy/dx = (y-2x)/(2y-x)

check your algebra.
 
  • #41
learningphysics said:
I'm getting dy/dx = (y-2x)/(2y-x)

check your algebra.

Wait I got

(2x-y)/(x-2y) = dy/dx

...
 
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  • #42
Because isn't it:

(2x-y) = dy/dx (x-2y)

and then you divide to get dy/dx = (2x-y)/(x-2y)
 
  • #43
antinerd said:
Because isn't it:

(2x-y) = dy/dx (x-2y)

and then you divide to get dy/dx = (2x-y)/(x-2y)

same thing. :smile: (if I multiply the numerator and denominator by -1, I'll get it that way)...

I took the dy/dx to the left side when solving, you took it to the right... it's the same answer.
 
  • #44
Pffsh. Equations don't have derivatives. Implicit functions do, however.
 
  • #45
ZioX said:
Pffsh. Equations don't have derivatives. Implicit functions do, however.

Your mom has derivatives.
 
  • #46
Don't be confused by the title of this thread

ZioX said:
Pffsh. Equations don't have derivatives. Implicit functions do, however.
Rest assured no one was trying to "differentiate an equation" :wink:
 
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