How Did 1886 Dutch Students Solve This Complex Math Problem?

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SUMMARY

The forum discussion centers on solving the equation $$\left ( a+x\right )^{2\over 3} + 6\left ( a-x\right )^{2\over 3} =5\left ( a^2- x^2 \right )^{1\over 3}$$ from an 1886 Dutch high school exam. Participants explore various algebraic manipulations, including substituting $$p = (a+x)^{\frac 13}$$ and $$q = (a-x)^{\frac 13}$$ to derive a quadratic equation $$p^2 - 5pq + 6q^2 = 0$$. The solutions for $$x$$ are established as $$x={ 7\over 9}\;a\ \lor\ x={ 13\over 14}\;a$$, with discussions on the implications of $$a \ge 0$$ and the quality of contemporary mathematics education.

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  • #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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