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

Entry: The Quadratic Formula - A2697311
Author: Beeblebrox - U556438

I did this in a maths lesson while I should have been working. I hope its useful.

Hello! (I should also be working, but what the hey!)

Nice Entry!

There's some problems with the formatting (a long scroll down after the first step in the last part). Writing formulas in h2g2 is indeed a bit complicated (there's no adequate sqrt sign, for example) - I'd suggest using the exponent of 1/2 instead of the sqrt sign - also, I'd suggest using italics for the variables, which is common mathematical notation.

Bye,

HELL

I see you are a newcomer to h2g2, so well done for offering an entry for peer review. Unfortunately, I do not like the style which says here is the answer, what was the question?

The description of the use of the formula may be a little condescending, as in my opinion, if you had developed the quadratic formula as the solution of a quadratic equation, the meaning of the symbols would be obvious.

I'll go silent now, and wait for other reviewers to chime in.

I think, to tone down what OH has said, is that you jump in straight away with the formula and don't give the reader any lead in. You have to remember that this entry will be read by people with a wide range of abilities, who may not even know what a quadratic equation is.

It might help to start with a bit of a literary introduction setting the scene about where you need the quadratic formula.

Hope this feedback is useful

Researcher PSG

Hi Beeblebrox,

I agree with the posts above re the way the entry launches into quadratics in a way that might confuse those who know little or nothing about them

Instead of
<<
... for some strange inexplicably (typo by the way ) reason you suddenly find yourself wanting to know the answer to the formula 3x²+7x-42=0 ...
>>
being almost at the end, I'd suggest moving this to the intro paragraph and rewording it to give an example of why/when/where/etc someone might want/need to know the answers, and then go on to show the formula



As for the square root symbol, try these:

&radic;

or



Cheers
six7s

I hate to have to chime in discordantly with the rest of the reviewers, but I agree completely with the comments made so far. You need to start off with a clear explanation of what a quadratic equation is and what the roots are. Then you need some clear but simple examples of equations that can be solved without recourse to the formula. *Then* you need to bring in the formula.

Hi, me again... I had a thought...

How about something on the history (the who, when, where, why etc) of quadratics? Then maybe go on to the 'what' and 'how'...

Like I said, just a thought

Hi 67s. I was already doing something on the history of quadratics (it's on my notebook, not on h2g2 yet). It leads *very* far, and is very intricate. May I ask to leave room for an Entry concentrating on the history? And let this one concentrate on the maths opf the formula? I think having both in one Entry is a bit much. What do you think?

HELL

Just one idea you might want to add to the entry, which is not very often mentioned, but which is most relevant to 'blind' use of the formula. If you have an equation, for example 2x²+40x-1=0, and are only interested in one root, say a positive one, then sometimes (as in this example) the result of using the formula can be far less accurate than one would hope - here it boils down to -10+&#8730;101.

You might want to mention how to get round this numerical difficulty.

cheers for all the help guys. I can see I've got a lot of work to do to the entry.

beeblebrox

How about, as an addendum, the fact that for those who want to try it out for themselves, one can in fact derive the quadratic formula by completing the square on the formula ax^2+bx+c=0?
Just a thought.

a good idea, I don't really like reading really long entries so having two separate ones would be good, especially if you've already started writing it.

History PR thread here: http://www.bbc.co.uk/dna/h2g2/alabaster/F48874?thread=456610&post=5648426#p5648426 HELL

Mysteriously no-one else seems to have noticed this so perhaps it's just me:

In the quadratic equation 'b' = 7 but in the quadratic formula you use to solve it 'b' = 5. Consequently your two solutions don't work.

F

Hi there!

I think this Entry is fine for a basic look at the quadratic formula, but if it is not, then I would like to see how the quadratic formula can be applied to practical situations... as the quadratic formula is used a lot graphically, perhaps a mention of this?

Also, perhaps you could give a small section to the discriminant part of the formula, on how if b²-4ac is greater than 0/less than 0/equal to 0 states the number of roots, which I think goes:

b²-4ac > 0 -> 2 roots
b²-4ac < 0 -> no real roots
b²-4ac = 0 -> 1 root

Perhaps also a mention that just because there are *no* real roots, the answer does not stop there, as though there are no real roots, it leads on to imaginary numbers... but that is a whole new kettle of fish

Which brings me on to my last point on how you can judge something as being 'fiendishly difficult', when I assumed that one use of the formula is when the normal ax² + bx + c = 0 cannot be factorised

Unless this is intended to be a simple guide, perhaps the bits about imaginary numbers can be left out, but I can't imagine the quadratic formula without at least a section on the discriminant, or factorisation You can spend ages trying to go through the formula, checking the roots when all you could have done was factorise or complete the square to solve the equation in hand

Sorry if I seem like I am being really harsh, but they are important aspects of this part of maths, and I think they need to be given at least a mention

I hope this helps!

Caper Plip

Still no clearer than when I tried A-level maths!!!

Minor formatting point (I feel qualified to comment on this!) your heading and sub heading “Uses of an equation” and “Example” seem like over-kill – surely one heading would do?

Good work – I’ll have to read it again when I have removed the pencil from behind my ear and set it to work!

Speller

I'd love to be proven wrong, but I fear Beeblebrox is not returning to this one.



HELL

Possibly you are right

no worries. i'm still here really, just been a bit busy recently trying to get broadband sorted out at home. but i'm coming back to it now.

Beeblebrox! Welcome back

HELL