h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

So do you mean that if you present your findings on a gragh you can work out a quadratic equation which will tell anyone what is the best quantity of water given to a plant?

Provided you use a quadratic function to model the curve, yes.

You could also use a sine function or some other function to model the curve.

HN

OK I am definitely bearing it mind at the moment but all I am doing is thinking how to put it into the entry without causing confusion.

Do you think I should include the example you have given or just explain what you have said?

I think I should read the other related entries that you have linked to before answering your question. Feel free to ping me if I don't get back to you by tomorrow your time, whatever that might me.

Happy

Nice work

Well, there are certainly a bunch of things in engineering that are quadratic - or parabolic (we just love those parabolas). The shape that a bridge takes, for example.

However, it occurs to me that a great example is the golden ratio. For any two things that we'll denote a and b (sides of a rectangle, lengths of string, etc) if they are in the following proportion (a+b)/a = a/b = phi, then they are golden, ratio-wise. Anyway, with a little fiddling one can express phi regardless of the values of a and b as follows:
phi^2 - phi - 1 = 0

and solving for phi can be left as an exercise, with the solution footnoted:
phi = (1+sqrt(5))/2

(here we've ignored the negative result (1-sqrt(5))/2 because it's not golden, but something else)

"In cases where the quadratic equation has a negative, you must reverse the addition to subtraction"

I've never heard this one before - surely you should just advise readers to use a negative value for 'b'?


Also, could you mention that quadratic formulas with 'a'=1 are easy to solve on sight? All you need to do is find two numbers that add to make 'b' and multiply to make 'c'.

Alex

>>All you need to do is find two numbers that add to make 'b' and multiply to make 'c'.<<

In practise however, you do that by solving the corresponding quadratic equation

"Also, could you mention that quadratic formulas with 'a'=1 are easy to solve on sight? All you need to do is find two numbers that add to make 'b' and multiply to make 'c'."

They're not all easy to solve on sight, x^2 + (pi)x + 79 wouldn't be easy to do by sight, for example...

no, not easy at all. in fact somewhat complex

Ok, some of them are easy.

Indeed. Some of them are easy, and can be solved by sight. However every quadratic equation can be re-written so that a=1 if you so wish. In many cases it's simpler just to dive straight in to the formula rather then spend ages trying to work out the factorisation, only to give up and resort to the formula in the end anyway.

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Another fine entry


Even it I didn't understand it

Though it's a useful attribute, I'm afraid that 'understandable by lil' isn't a prerequisite for an entry being accepted

JHawkesby

Thankyou so much everybody.

Oh, I forgot the



*hic*

Hey congratulations!

I've been idly wondering - if for some reason I were to feel threatened by quadratic equations, would I be a quadratophobe, or a quadratiphobe? And would I feel comfort knowing that there's a word for my unease? Lil?

Quadrophobia

An irrational or unjustified (and often uncontrollable) fear (and sometimes terror) of things that come in fours


Hey! I only suffer from the plague of lilitis, Paily!