How Did 1886 Dutch Students Solve This Complex Math Problem?

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Homework Help Overview

The discussion revolves around solving a complex algebraic equation from an 1886 Dutch high school exam, specifically $$\left ( a+x\right )^{2\over 3} + 6\left ( a-x\right )^{2\over 3} =5\left ( a^2- x^2 \right )^{1\over 3}$$. Participants express their astonishment at the problem's difficulty and share their attempts to understand the solution process.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss various algebraic manipulations, including dividing both sides of the equation and rewriting terms. Some express confusion about the steps and the implications of dividing by certain expressions. Others suggest using substitutions to simplify the equation.

Discussion Status

The discussion is ongoing, with participants sharing different approaches and questioning each other's reasoning. Some have offered insights into potential methods, while others are still grappling with the algebraic complexities involved.

Contextual Notes

There is a notable emphasis on the historical context of the problem, with some participants reflecting on the perceived decline in high school math education standards. Additionally, questions about the constraints on the variable \(a\) and its implications are raised, particularly regarding the condition \(a \ge 0\).

  • #31
Frabjous said:
So what? You get one value of x for one value of a. The OP has the solution which has TWO values of x for a given value of a. The OP also has the solution for other values of a. You are missing a lot of solutions.
I will check if I can get other values by changing my ##m## value. Cheers man!
 
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  • #32
You are going to come up with a finite number number ‘n‘ of solutions. Given that there are an infinite number of solutions, your grade for the problem will be n/∞=0. :wink:
 
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  • #33
@chwala ,
Your response to my post (#22), although I made a mistake in that post of mine. It is corrected here:
SammyS said:
(My post (#22) in reference to your post (#19) )
It looks like you intended to divide both sides buy ##(a+x)^\frac{1}{3}## but you neglected dividing ##5(a-x)^\frac{1}{3}## by ##(a+x)^\frac{1}{3}## .

Correction:
... you neglected to divide ##6(a-x)^\frac{2}{3}## by ##(a+x)^\frac{1}{3}## .

Your post(#23)
chwala said:
This may be unorthodox approach but hey let us do it!

We have,

##(a+x)^{\frac{2}{3}} + 6 (a-x)^{\frac{2}{3}}=5(a^2-x^2)^{\frac{1}{3}}##

I will still let

##m=a+x##

and

##k=a-x##

then,

##m^{\frac{2}{3}} + 6k^{\frac{2}{3}}=5m^{\frac{1}{3}}k^{\frac{1}{3}}##
(I'll cut in here.)

This looks fine. In fact you could write that as;

##\displaystyle m^{\frac{2}{3}} -5m^{\frac{1}{3}}k^{\frac{1}{3}}+ 6k^{\frac{2}{3}}=0## ,

which can be factored quite nicely, by the way.

You then go on to state;
##6k^{\frac{2}{3}}=m^{\frac{1}{3}}[5k^{\frac{1}{3}}-m^{\frac{1}{3}}]##

Let

##m^{\frac{1}{3}}=1##

then,

##6k^{\frac{2}{3}}-5k^{\frac{1}{3}}+1=0##
...

the other steps to solution shall remain as shown on the quoted post.

cheers!
Although you get the same quadratic equation as you did in the "quoted post" (#19), that is only due to the choice of ##m=1##.

For other values of ##m##, posts 19 and 22 will not agree.
 
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  • #34
SammyS said:
@chwala ,
Your response to my post (#22), although I made a mistake in that post of mine. It is corrected here:Your post(#23)
(I'll cut in here.)

This looks fine. In fact you could write that as;

##\displaystyle m^{\frac{2}{3}} -5m^{\frac{1}{3}}k^{\frac{1}{3}}+ 6k^{\frac{2}{3}}=0## ,

which can be factored quite nicely, by the way.

You then go on to state;

Although you get the same quadratic equation as you did in the "quoted post" (#19), that is only due to the choice of ##m=1##.

For other values of ##m##, posts 19 and 22 will not agree.
Thanks can see that we end up with what was previously found by other members:

... i.e

##x^2-5xy+6y^2=0##

##(x-2y)(x-3y)=0##

...

where;

##x=m^\frac{1}{3}##

and

##y=k^\frac{1}{3}##
 
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  • #35
Mark44 said:
Based on @vanhees71's subsequent response, he evidently meant "integration by parts." It's possible that he conflated the names of the techniques of integration by parts and integration by partial fraction decomposition.
I think it's a "Germanism", because in German we call this technique "partielle Integration". Obviously in English it's exclusively called "integration by parts".
 
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