MHB What is the Differentiation Challenge?

AI Thread Summary
The discussion centers around a mathematical problem involving the equation \(\frac{x - y}{x + y} = \frac{x + y}{y}\) and the task of finding \(\frac{\mathrm{d}y}{\mathrm{d}x}\). Participants are encouraged to present their solutions in various forms, such as \(\frac{\mathrm{d}y}{\mathrm{d}x} = f(x, y)\) or \(\frac{\mathrm{d}y}{\mathrm{d}x} = g(x)\). The term "challenge" is playfully questioned, with some participants suggesting that the problem is meant to be light and not overly complex. The thread emphasizes the enjoyment of solving problems at different difficulty levels, inviting contributions from those who find the problem engaging. Overall, the discussion promotes collaborative problem-solving in a friendly atmosphere.
Theia
Messages
121
Reaction score
1
Let's have a snack challenge for a while. ^^

Let $$x$$ and $$y$$ be real numbers (with restrictions $$y \ne 0, \ y \ne -x$$) and $$\frac{x - y}{x + y} = \frac{x + y}{y}$$.

Find $$\frac{\mathrm{d}y}{\mathrm{d}x}$$ in whatever form you like most. I mean, for example forms $$\frac{\mathrm{d}y}{\mathrm{d}x} = f(x, y)$$ or $$\frac{\mathrm{d}y}{\mathrm{d}x} = g(x)$$ are equally good at this time.

Please remember to use spoiler tags when you run to post the answer! :)
 
Mathematics news on Phys.org
How is this a "challenge"?

Once you have multiplied on both sides by y(x+ y), it is a straight forward Calculus I "implicit differentiation".
 
Last edited by a moderator:
HallsofIvy said:
How is this a "challenge"?

Once you have multiplied on both sides by y(x+ y), it is a straight forward Calculus I "implicit differentiation".

I said this is 'a snack', not 'an afwully complicated thing you need to think about seven years'...
Anyway, then you can show me your answer, right? ^^
 
Theia said:
I said this is 'a snack', not 'an afwully complicated thing you need to think about seven years'...
Anyway, then you can show me your answer, right? ^^

We appreciate challenge problems of virtually any level of difficulty. My advice to everyone is that if you find a posted problem "too easy" to solve, then leave it for those who will be challenged by it and enjoy posting a solution. :D
 
My solution:
$\d y x = \text{Undefined}$

Yummy snack! ;)
 
I like Serena said:
My solution:
$\d y x = \text{Undefined}$

Yummy snack! ;)

That's right! Can you give a short explanation too, please? :D
 
Theia said:
That's right! Can you give a short explanation too, please? :D

Sure! (Bandit)

$x$ and $y$ are given to be real numbers with $y\ne 0$ and $y\ne x$.

We have:
$$\frac{x-y}{x+y}=\frac {x+y}{y} \quad\Rightarrow\quad
(x-y)y=(x+y)^2 \quad\Rightarrow\quad
2y^2+xy+x^2=0 \quad\Rightarrow\quad
y = \frac 14 (-x\pm \sqrt{x^2 - 8x^2}) =\frac 14 x(-1\pm i\sqrt 7)
$$
Since $y\ne 0$, there are no real numbers $x,y$ that satisfy the equation.

Therefore $\d y x$ is not defined anywhere. (Cake)
 
Well done! Thank you! ^^

And now, I'd think I try to be more careful when it comes to 'implicit differentiation'... :D
 
Back
Top