For the mathematicians among you...

[raven]

I need help. Not psychiatric help, though that might also be of use at this moment. No, I need help with maths, and I know I have some very clever mathmos hanging round these parts, so here goes:

First of all, either the rules of mathematics have changed since this morning or I'm missing something really obvious, but my calculator persists on telling me that -3² is -9. Surely this cannot be right? Or am I making some elementary mistake?

Possibly related to the above, I'm having issues with the next bit, which asks me to graph this horror of an equation:
y=(1/4)x²+(1/2)x-1 for integer values of x from -5 to 5. Edit: Have tried to tidy equation and put brackets in right places.

So, as I learned at GCSE many many years ago, I have made myself a table of values. And given the above integer values of x, I have got a sequence of values for y as follows: 2.75, 1, -0.25, -1, -0.25, -1, -0.25, 1, 5, 7.75. Is there some peculiar feature of quadratics I've missed, because I really don't think that's right. I do so hate being mathematically illiterate, but there you go.

And mathematically illiterate I shall have to remain, because I have four books on Mill to read tomorrow, four thick Politics books to read for Monday, notes to be made on all of them, plus a 2500 word essay on decision-making in the British executive. Therefore I'm missing poker night tonight. And no, I haven't procrastinated at all. I haven't dared.

Actually, this is mostly the fault of whoever it is who can't remember my email address, because I got Politics two days late and my maths not at all, as my maths tutor appears to have no idea who I am and no-one thought me important enough to go to the effort of forwarding me the information. So this is why I'm doing maths now, and Mill later, and politics all day tomorrow and most of the weekend.

(Also: I owe one ficathon story. It's really late, but I'm afraid I'm going to have to let it be even later, because I can't, I really can't do it right now. I hope you understand.)

This was meant to be request for help, not a rant. All I do lately is rant, cry and sleep. I've apparently eaten nothing but apples and cashew nuts for the last two days, and not even noticed.

Yes, I'll go away, I'm sure I'm not making anyone's life any brighter.

Edited again: Yes, I'm still miserable. But I have nailed the equation: x=3.2 or x=1.2. Not exactly - it's only roughly where the bizarre wobbly curve crosses the x-axis, but fed into the original equation, -3.2 yields 0.04 and 1.2 yields -0.04. Good enough.

Comments

[shipperkitten.livejournal.com]

Do you mean (-3)^2 instead of -(3^2)? If you're just typing in -3^2 it takes it as the second, and leaves the minus sign out of the squared bit.

[loneraven.livejournal.com]

I mean the former, but I sort of assumed that it was taken as read that that's what I meant, if it makes sense. It's definitely (-3)² and not -(3²) that I'm after.

Ah, the answer comes out right if I put the brackets in. I'll remember that.

[tomkerswill.livejournal.com]

Yeah... all calculators do stuff in this order I think: brackets, squared, of, divide, mulitply, add, subtract.

[gamesiplay.livejournal.com]

Nope, that's technically correct. (-3)^2 is 9, but without the parentheses, I'm pretty sure your calculator's reading it by default as -(3^2), which would be -9.

[gamesiplay.livejournal.com]

Still thinking about that quadratic thing; just woke up and am not too quick on the uptake. I'm sure someone else will help you on it first anyway, given that I was already beaten to the punch on the first question. :)

[loneraven.livejournal.com]

I love having a mathematically inclined flist. :) I think you and shipperkitten have nailed the first problem in any case. Have just been informed that the above equation is not a quadratic, as a, b and c are not integers. Waaah.

[gamesiplay.livejournal.com]

The problem's not that they're not integers, since it's acceptable to have non-integral coefficients. The problem is (possibly) the placement of the x. Are you reading it as y=1/(4x)+1/(2x^2)-1 or y=(1/4)x+(1/2)x^2-1? That's what could make a difference, having the variable in the denominator. At least that's how I remember it.

[gamesiplay.livejournal.com]

Ignore this. You answered me below. :) Now I'm just being overzealous, because I haven't done math in too long and I kind of crave it. (God, that's frightening.)

[biascut.livejournal.com]

Hee! That's exactly what I'm doing!

I have promised myself that one day I will finish my A level Maths. They'd just better not get rid of A levels before I get round to it.

[shipperkitten.livejournal.com]

LOL, you can explain things way better than I can!

And I've been awake all day and don't like the look of that equation. ;)

[gamesiplay.livejournal.com]

Hee, but you figured out the denominator problem with the second question first!

(Iona--is it supposed to be a quadratic, according to the problem? In that case, you should handle it as (1/4)x+(1/2)x^2-1. If not, as said above, it shouldn't be a quadratic if the variable's in the denominator, so your y-values shouldn't look like they're quadratic and you're okay.)

[loneraven.livejournal.com]

Not necessarily, I just assumed it was one. That's a relief; if it isn't a quadratic, I have no idea what it's supposed to look like, but not a U-shaped curve. So unless my calculation is off at any point, I'd hope the values are okay.

[shipperkitten.livejournal.com]

Second question I should probably know but can't see it at the moment (supposed to be revising for a maths exam tomorrow morning, it is eating my brain)!... all I can say is it's not a quadratic as the x terms are on the bottom not the top.

[that_mireille]

It's a quadratic, just with rational coefficients rather than integral ones. It may look "better" if you write the coefficients as fractions: y = .25x + .5x^2-1. Same equation.

[shipperkitten.livejournal.com]

I took it to be exactly as written above, which was 1 over 4x and so on (rather than a quarter of x) which would make it totally different.

[loneraven.livejournal.com]

Sorry, it is a quarter of x! I should have been clear. Written out, it's 1/4 and then x.

[that_mireille]

From the way it's written (1/4x) there's no way to tell whether it's (1/4)x or 1/(4x), except from the fact that it's apparently meant to be a quadratic.

[loneraven.livejournal.com]

Having realised this belatedly, I've edited to that effect.

[quackaquacka.livejournal.com]

I have no idea on the maths, but I'm sorry you're feeling so bad.

[eternalwings.livejournal.com]

Ditto.
Though the maths makes my head hurt *pout*

[loneraven.livejournal.com]

Mine, too. :)

[loneraven.livejournal.com]

Thanks. *hugs*

[biascut.livejournal.com]

I shall be fascinated by the responses to this! I love maths, but haven't studied it for yeeears. Here's my attempt (Grade B AS level Maths, 1996!):

-3² is very definitely +9, so I'm not sure what your calculator is on. I think it's giving you -(3²), so it's working out the square of a positive number and then making it a negative value, rather than giving you the square of a negative number. Unfortunately, I can't remember how to tell a scientific calculator to give you the square of a negative number (except by doing [3] [+/-] [x] [3] [+/-] [=]). How's it getting on with -2²? +4 or -4?

Quadratic equations are generally smiley faces, but perhaps there something about having a value of X2<1 which means that it has a wobble in the middle? Alternatively, are you doing the 1/2x2 in the right order - I think it should be (X x X) x 0.5. If you're doing (0.5 x X)2, that would account for some weird results?

Right! Now let's see what the real mathmaticians have to say!

[biascut.livejournal.com]

X2<1

Sorry - meant the fact that it's 0.5 of X², rather than a whole number. I think it's more likely to be the brackets in the wrong places, though.

[loneraven.livejournal.com]

I'm glad to provide maths for you! :)

I'm doing it in the right order - ie, X x X x 0.5 - so it can't be that. The real mathematicians are making me cry.

[that_mireille]

The problem with the quadratics probably is putting the brackets in the wrong places, or not putting them in and your calculator interpreting things wrong.

I did it on paper, and made multiple columns: x, x^2 [can't be bothered to do superscript HTML], 1/2*x^2, 1/4*x, 1/4 x + 1/2 x^2, y, so that I could keep track of what I was doing.

And for x = -5, I got:

x = -5.
x^2 = 25.
1/2x^2 = 12.5
1/4 x = -1.25.
1/4x + 1/2x^2 = -1.25 + 12.5 = 11.25
y = 11.25 - 1 = 10.25.

[loneraven.livejournal.com]

I think you're right. I just don't know where I've gone wrong; perhaps if I do it in my head rather than subjecting myself to the calculator, it won't go wrong, but I don't think I have the time for that.

Thanks for helping. :)

[hathy-col.livejournal.com]

I understand not a word that was written there. I am more mathematically illiterate than you, but look on the bright side - they're teaching me maths in Spanish. Oh, god, I wish I was joking. LIKE BOTH THINGS WEREN'T INCOMPREHENSIBLE ENOUGH.

However, I do understand that you need much in the way of hugs. I am bringing food when I come because I will make you eat if it kills me.

[loneraven.livejournal.com]

Hee. Not quadratics, I hope, although I'm sure they have a much better word for them.

I'm so looking forward to seeing you! Gleee. And food is good.... in theory. *blink* I forgot to have dinner again.

[hathy-col.livejournal.com]

Not quadratics. I do know how to say 'squared' in Spanish, though. Well. I should but note my lack of vocab knowledge.

I WILL BRING FOOD. *makes a note to Do The Tescos Thing before she leaves tomorrow* Cheese, bread and butter. It's all a student needs for a week. Add a toastie maker, mushrooms and onions and you're sorted ALL TERM. (not joking. Greatest toastie known to man and now known throughout the world or at least my house as THE TOASTIE OF AWESOMISITY. Sauces optional - I like brown, Katie has an unhoy glee in sweet chili sauce...)

Dinner is important, dear. Keep on trying to have it.

[gwynnega]

Sorry you're having maths woe (or math woe, as we would say in the States). I hate maths! ::hugs::

[loneraven.livejournal.com]

*cling* I hate maths, too!

[tau_sigma]

All I do lately is rant, cry and sleep. - *hugs* many many times. Aw. I wish I could help.

From what other people have said, your calculator appears to be a little strange ... my calculator gives -3² = 9. Anyway.

As to the second problem ... a few simple things I can say are that it crosses the x-axis at about -1.686 and 1.186, and the y-axis at -4. I think that's the easiest way to do quadratics, and then from those three points you can draw the curve ('concave up,' as my calculus lecturer says, if the x² term is positive, 'concave down' if it's negative - surely concave up and down are tautologistic or something? Shouldn't it be concave and convex?) If it would help, I can graph it tomorrow on the library computers (I don't have the program here) and post/e-mail you the graph so you can check your graph against it?

You make all our lives brighter! *hugs again*

[loneraven.livejournal.com]

It does seem strange. As they've said, I can only assume that it parses -3² as -(3²).

Thanks so much for offering, but I have to hand this in tonight. I think I've nailed it, though - I hope, anyway. The solutions don't yield exactly 0, but I'm choosing to blame the graph rather than the method.

*hugs* *clings* I don't feel bright, I tell you. I'm just a mess at the moment.

[me-and.livejournal.com]

I suddenly became interested then (flist is a bit boring), but everyone else seems to have answered the questions already. Damn.

[loneraven.livejournal.com]

So sorry to disappoint. Bloody mathmos. :)

The lanky bugger

[(Anonymous)]

if you've got excel you should be able to get the computer to draw it for you, then just copy - f.maths taught me well :-)

[thiswaltz.livejournal.com]

*sends you virtual comfort food and hugs* I can see why you're stressed- that's a mind boggling amount of work. you're very brave for trying to tackle it, i know i couldn't.

you're math problem ther is worrying to me. I think i was supposed to have covered something like that last year, yet it looks like pure gibberish to me.

[loneraven.livejournal.com]

I can't, either. *groan* *eats comfort food* Thank you.

And it's gibberish to me too! *shakes head*

[amchau.livejournal.com]

I think it may be impossible for these comments to be mathier. However, I'll try dropping some random numbers in, not because I think they'll help (I'm useless at maths) but to try and pretend I'm not talking about something completely different.

When can I (7+2=9) telephone you? I'm tempted to try taking potshots this evening (7:30 to 8:30 is 1 hour and something in that time would suit me), but I'd like to know I'm not shooting in the dark, if you see what I mean. I want to talk about life, logic (but only if you want to), and next Thursday/Friday.

[loneraven.livejournal.com]

About eight would suit me (might still be out at seven* thirty). Clare will be here too, so expect squee!

I've been neglecting you shamefully and I'm really sorry. It's just the work, really: you're much more interesting than PPE!

*See, numbers in words for your benefit! :)

[amchau.livejournal.com]

Okay, I'll try and call about eight.* Whee! Clare!

I don't mind, so long as I know you haven't totally forgotten me. :)

*Thank you. It's very reassuring.

[loneraven.livejournal.com]

Rhiannon - hope you get this in time - please call about ten past eight, rather than eight? Sorry to be a pain; it's just Clare's train is late and I won't be back in time for your call.

[amchau.livejournal.com]

I've just checked my e-mail while listening to the posh woman tell me that "the person you have called in unavailable and does not have a mailbox", and am glad to discover this comment. I'll call again in ten minutes or so.