Maths!

philologos

maths maths maths maths
what do I have to learn for tomorrow

Irishstabber

the first 6 questions in paper 1

Strokesa

Yeah...what would be the best stuff to revise?

Irishstabber

Well I'll have my hands full with algebra algebra algebra...damn I HATE ALGEBRA :mad:

Mysteryfish

Really? I love algebra! It's completely pointless as i'm never going to use it later in life but its easy! What I hate is geometry! I can never work anything out. And no matter how hard I try my incircle nver touches all 3 sides. :-( Anyway, I'm just glad we have the weekend to study for paper 2.

As far as paper 1 goes, don't forget to revise tax and VAT and interest as sometimes, the simple questions have a twist in them that can throw you.

Irishstabber

Roll on Paper 2...Trigonometry, Geometry all my favourites

Mysteryfish

damn your mathamatical brain!

Strokesa

Thanks.
I really need to go study, yet im still here.
My stupidity ASTONISHES me, why have i no willpower?

Irishstabber

Mysteryfish wrote:

damn your mathamatical brain!

haha lmao I bloody wish :cool:
I just enjoy trigonometry, believe it or not...I love finding the angle degree of well angles in geometry.

Mimikyu

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Strokesa

Oh dear. I do honours and i cant do that...
How did u get x?

Hugh Hefner

I got x=2.84 and so on. Not 3. You just do a simultaneous equation. And then to find y just take one of the equations and substitute x for it's value.

Strokesa

Usually when i do simultaneous equations its all nice and straightforward with no decimals...i hate decimals they hurt my brain!

Mimikyu

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Hugh Hefner

Oh right sorry, I was being a complete idiot and was doing 2 x 9 = 19. *slaps self*

Strokesa

Bravo bravo. U should be in honours.
Or at least i should be in pass...

Mimikyu

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Flashling

Well, if all your working out is correct, the last bit definatly is, you're right.
For Math, learn line equations and laws of indicies, and theorums. Thats all really, though as Mysteryfish said maybe look over VAT? And BTW Mystery, algebra is great.

Mimikyu

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modular

The second part of the question is way easy.

You have x=3, so just substitute 3 for x in one of the original equations.

Take the first one: 2x-3y = 9

So:
2(3) - 3y = 9
6 - 3y = 9
-3y = -3

y = -1.

Mimikyu

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Hugh Hefner

modular wrote:

The second part of the question is way easy.

You have x=3, so just substitute 3 for x in one of the original equations.

Take the first one: 2x-3y = 9

So:
2(3) - 3y = 9
6 - 3y = 9
-3y = -3

y = -1.

Whoops a daisy. Looks like someone made a booboo. It's:-

2(3) - 3y = 9
6 - 3y = 9
-3y = 3
y = -1

modular

Hugh Hefner wrote:

Whoops a daisy. Looks like someone made a booboo. It's:-

2(3) - 3y = 9
6 - 3y = 9
-3y = 3
y = -1

That's one way of looking at it, yes.

You know what I meant.

Mysteryfish

Solitaryman666 wrote:

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Wait, isn't 4x-15x=-11x ? Or has my brain gone crazy? Am I missing something here?

modular

No, he's subtracting the lower from the upper, so is switching all the signs around.

Mysteryfish

but you add in simultaneous equations. hence the 57.
therefore, 4x+(-15x)=4x-15x=-11x

Fobia

Mysteryfish is right here, I was going to post but I didn't having said I wouldn't yesterday...

You add simultaneous equations, not subtract. If he had subtracted then he would have gotten 12y rather than 0y, a mistake many people make is using the term "cancelled", numbers don't magically vanish, there have to be none of them less, an idea is to write it out as 0y then simply take that out of the next line of your sum...

Back to the original question, one thing I notice is that Solitaryman666 wrote two different signs for the second equation in different posts, one must be right and one must be wrong...I havent time to figure out which is which atm so umm...good luck

modular

4x - 6y = 18
-15x - 6y = -39

He changes it mentally to:


4x - 6y = 18
15x + 6y = 39 (multiplied by -1)

---

19x = 57


so x = 3.

You can add OR subtract with simultaneous equations.

Mysteryfish

right so. I dunno, my brain is slowly desintegrating into nothing. I just got really confused for a moment. thanks for unconfusing me!

Nietzschean

there is quite a few ways of doing simultanious equations, it really depends what your given as to which is easier, i'm guessing the only 2 ways on the JC course would be substitiution and addition/subtraction as above.

In this case:
2x-3y = 9 (i)

5x+2y = 13 (ii)
Either would do, method one would give
x = (9 + 3y ) / 2 (iii)
which in eqn (ii) gives 5 ( (9+3y)/2) +2 y = 13
(multiply everything by 2 , and multiply in the 5 :
45 + 15 y + 4y = 26
19y = -19
y = -1
then putting this back in eqn (iii) gives x = 3.


The other as outlined before would be simplest by multiplying eqn (i) by 2 and (ii) by 3 and adding them,
one could also go 5 times (i) minus 2 times (ii).

Hugh Hefner

The way I do them is (using 666's example):-

2x-3y = 9 ===> 4x-6y = 18
5x+2y = 13===>+15x+6y = 39
......................19x+0y = 57
.......................x = 3


...................... 2(3)-3y = 9
.......................6-3y = 9
.......................-3y = 3
.......................y= -1



My way just seems less fiddly. Maybe I'm wrong. Anyway, the night before the Junior Cert. is probably not the best time to mention this.