MHB Geocaching: Solve a+b=c c/b=b/a Problem

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The discussion revolves around solving a mathematical problem related to geocaching, specifically finding the distance of AB given the proportions of AC:BC and BC:AB. The equations c = a + b and c/b = b/a are established as foundational relationships. Participants express confusion over the calculations and seek simplified formulas, particularly for variable b. The Quadratic Formula is mentioned as a method for deriving solutions, emphasizing the importance of demonstrating mathematical processes. Ultimately, the conversation highlights the challenge of determining specific distances without actual values, focusing instead on the relationships between the variables.
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I love geocaching and a problem that recently came up is:

A--------------B------------C (not to scale)

Find the distance of AB if the proportion of AC:BC is equal to BC:AB. Substituting a for AB, b for BC and c for AC, I come up with:

a+b=c where c/b=b/a

I'm at a loss here. When I put it in WA it comes up with the answer (although looking at the answer, I have no idea how it calculated it) and I was able to "brute force" my answer as well and get the right answer (thanks Excel) but I want to know the math behind it. The actual values are irrelevant as I want to get to the simplified formulas.
 
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Surely, you realize that you can't determine the actual distance from A to B knowing only proportions?

What, exactly, did you put into WA?
 
You have relationships. Without actual values, that's all you have.

c = a+b -- good

c/b = b/a -- good

You could also write $\dfrac{a+b}{b} = \dfrac{b}{a}$

You could also write $a^{2}+ab = b^{2}$

You could also write $(a-b)^{2} = ab$

You could also write: $a = \dfrac{b}{2}(\sqrt{5}-1)$

Which simplified formulas would you like?
 
tkhunny said:
You have relationships. Without actual values, that's all you have.

c = a+b -- good

c/b = b/a -- good

You could also write $\dfrac{a+b}{b} = \dfrac{b}{a}$

You could also write $a^{2}+ab = b^{2}$

You could also write $(a-b)^{2} = ab$

You could also write: $a = \dfrac{b}{2}(\sqrt{5}-1)$

Which simplified formulas would you like?

Can you simplify for b please and show the work? I don’t know where the $\sqrt{5}$ comes from.
 
TheCricketer said:
Can you simplify for b please and show the work? I don’t know where the $\sqrt{5}$ comes from.

This is where you get to demonstrate your love of mathematics. I used the Quadratic Formula with the expression immediately above. There are a few other ways to do it. Show your work!
 
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