are u allowed to use 4u techniques on a 2u paper? (2 Viewers)

[buchanan]

I'm sure I remember my maths teacher telling us that you can't use complex numbers in a 3 unit paper.

This is why universities want to get 100% of their students from overseas, or from the IB, not the HSC. They are only stopped by stupid politicians. These stupid rules mean that by international standards, the HSC is crap!

No wonder some private schools are threatening to go 100% IB!

 

[Estel]

This is why universities want to get 100% of their students from overseas, or from the IB, not the HSC. They are only stopped by stupid politicians. These stupid rules mean that by international standards, the HSC is crap!

No wonder some private schools are threatening to go 100% IB!

lol
They're doing it for publicity.

The 2U does a remarkably good job at giving a vision (albeit fogged up) of mathematics.
And Pender himself notes how the pieces all come together to create a pretty good syllabus...
What agenda do you have?

 

[Slidey]

I may be wrong, but I'm sure I remember my maths teacher telling us that you can't use complex numbers in a 3 unit paper. For example, if you're solving an equation and end up with x = square root of something negative, you have to say that there are no solutions and not continue on using i's etc.

I used complex numbers today to prove cos3A=4cos^3(A)-3cosA. Let's see if I get marked down. It was just the quickest method I could think of.

 

[Estel]

lol
are you coming first with a massive margin or something?

 

[Captain pi]

I managed to get complex numbers into a 4u exam by using completely the wrong, strangest method on earth, the real question is how I managed to get the correct answer! (through doing it correctly, I know I did). I realize now what I did.

The question was something like this:
If the cost of making a certain trip in a vehicle is given by C=2V + 392/V, where, V= the average speed of the vehicle. Find the speed which will give the cheaps trip. Worth 3 marks out of a shitload (probably 100, cant remember)

Simple question, all you do is differentiate C, find the minimum point, SO....
I differentiated C, and got....... C'= 2 + 392 {my error lies here, differentiate first term, integrate the second.......SHIT, maybe I should join general now}
but, that doesnt let me find the minimum turning point, it just gives me a constant, wtf?
So, after decided I was correct and the exam must be wrong, decided to try make C=0 and solve for V.
2V^2=-392,
V^2=-196,
V=14i,
test V=14, C=56
V=13, C=56 + 2/13
V=15, C= 56 + 2/15
so, V=14, cheapest trip
COMPLETELY INCORRECT, BUT CORRECT ANSWER.
It was about 2 minutes after walking from the exam that I realized I integrated and messed up doing the correct, first method with C'. I'm so embarrassed about the stupidness of my mistake, but, did I invent a new way to solve the question, or is it just a fluke ended up with the right answer?
We'll have to wait see what my teachers get out of it. I'm devastated that I threw out the bit of paper with my C'=... attempt, so now they'll just think I didnt know how to do the question, when I really did, just screwed up. STAPLE ALL WORKING OUT EVEN IF ITS SCRAP TO THE EXAM, IT COULD HAVE MARKS, EVEN IF YOU THINK YOU'RE WRONG!!!! I learnt the hard way!

(The integral of 392/V w.r.t. V is 392ln|v| +c not 392; you can't divide by zero.)

If you get a single mark for this question (even if you stapled your incorrect differentiation) I'd consider yourself as slipped through the cracks.
I'd say the criteria would be:

1 mark for correct differentiation
1 mark for finding dC/dV = 0 i.e. V = ±14
1 mark for finding minimum turning point and conclusion ("Minimum cost iff V = 14." [are you sure that's right? sounds mighty slow to me!].)

If you get a mark for correct answer, I'd be mighty indignant if I were a fellow student: marks should be awarded for steps, not answers.

Your method jumped from V = 14i (which should have been immediately rejected (unless you're talking about electromagnetic waves, which, admittedly, the question did not exactly refute )) to saying V = 14. That's not an sound argument.

Also, I fail to see how you, by testing V = 13, 15, concluded that V = 14 is the maximum. I don't contest V = 14 is the correct answer, but your syllogism is unsafe for public use.

Adieux.

 

[HayleeKate]

(The integral of 392/V w.r.t. V is 392ln|v| +c not 392; you can't divide by zero.)

If you get a single mark for this question (even if you stapled your incorrect differentiation) I'd consider yourself as slipped through the cracks.
I'd say the criteria would be:

1 mark for correct differentiation
1 mark for finding dC/dV = 0 i.e. V = ±14
1 mark for finding minimum turning point and conclusion ("Minimum cost iff V = 14." [are you sure that's right? sounds mighty slow to me!].)

If you get a mark for correct answer, I'd be mighty indignant if I were a fellow student: marks should be awarded for steps, not answers.

Your method jumped from V = 14i (which should have been immediately rejected (unless you're talking about electromagnetic waves, which, admittedly, the question did not exactly refute )) to saying V = 14. That's not an sound argument.

Also, I fail to see how you, by testing V = 13, 15, concluded that V = 14 is the maximum. I don't contest V = 14 is the correct answer, but your syllogism is unsafe for public use.

Adieux.

You're absolutely right, my method doesnt even exist, let alone make sense, it was completely illegitimate, but who knows, i think knowing my teachers i'll probably get at least one mark though (but, i am teachers pet, so maybe others wouldnt), doesnt matter, prolly 100% for rest of the exam. What was i thinking (?!?!?!?!) when doing this question I wonder....
Embrace your inner idiocy.

 

[thunderdax]

with the original question we had this question in a 3U exam asking for the poly. with roots a^2, b^2,c^2 given a poly with roots a, b, c. Really easy question for a 4U person but really hard for a 3U.

 

[Dumsum]

Edit: never mind, read q wrong.

 

[Emma-Jayde]

We were told we can't use complex numbers to solve a 3u question. For eg, say you're doing a polynomials question and end up with
x^2 + 16 (yeah easy enough to sketch I know)
you wouldn't factorise it to end up with complex roots-it isn't part of the 3u syllabus and the paper will be marked according to that.
Or if you end up with a negative under the square root sign, you leave it there and don't take it any further.

 

[HayleeKate]

We were told we can't use complex numbers to solve a 3u question. For eg, say you're doing a polynomials question and end up with
x^2 + 16 (yeah easy enough to sketch I know)
you wouldn't factorise it to end up with complex roots-it isn't part of the 3u syllabus and the paper will be marked according to that.
Or if you end up with a negative under the square root sign, you leave it there and don't take it any further.

Its different, if you're using the 2u method, of course you're not expected to take it to the next level using complex's and stuff, but, does that mean you're not ALLOWED to use a different 4 technique? Just because you dont factorize (x^2 + 16), youre not expected to and the question is over there, but that doesnt mean you cant use a 4u thing within the working of another question, if you end up with the same answer, just different, higher level method (usually more difficult, but if its all you remember, better than nothing).

 

[haboozin]

if you make a mathematically correct statement (working out) to gain an answer to a specific problem, it will be marked correct.

The only limitations with such statements are that you can't use the crappy physics equations that are built for like kids.

Unless the question makes specific comments of what method to use (eg: use the first principle to differentiate x²)

However, in most cases it will not be necessary to use 4unit methods in 3unit questions (except for Integration) this is because usually the questions lead you up using 3unit rules (this is mainly in graphs) in 3unit they will ask you: find the turning point and determine its nature.
and then Qiii will be to sketch the graph so no 4unit technique is needed to sketch such graphs.

 

[Slidey]

Also remember that even if they do lead you into the question, specifying what method to use, but then go no to say "hence or otherwise", you can use whatever method you want.

 

[mysteek]

for last years hsc, i called the HSC helpline thing and they said that you shouldnt have to use 4unit techniques in a 3unit exam, but it is ok to do so, if you get the correct answer, then they will give it. In school exams, they might not give u marks. u should aviod using them but if you cant get the answer using 3unit techniques, then might as well use 4unit techniques. for 2unit, im assuming the samething but to make sure, call the HSC helpline when it opens up

 

[fantasy27]

the only 4u sort of thing that we actually used in our exams or just simple class work was use 'implicit differentiation'.. and teacher said that was okay if we were to use it in the hsc, but to specificially say "by differentiating implicitly"...

 

[JamiL]

with the original question we had this question in a 3U exam asking for the poly. with roots a^2, b^2,c^2 given a poly with roots a, b, c. Really easy question for a 4U person but really hard for a 3U.

beg 2 differ mate, simple for both 3 and 4u
unless my teacher taught my 3u class a 4u method..

 

[JamiL]

for last years hsc, i called the HSC helpline thing and they said that you shouldnt have to use 4unit techniques in a 3unit exam, but it is ok to do so, if you get the correct answer, then they will give it. In school exams, they might not give u marks. u should aviod using them but if you cant get the answer using 3unit techniques, then might as well use 4unit techniques. for 2unit, im assuming the samething but to make sure, call the HSC helpline when it opens up

the only thing in 2u i could even think of you would use 4u stuff in, is if they give u a hard 2u graph question. u may be able 2 use 4u methods like impliced differeciationm but i highly doubt it.
if u had a polynomial (ie a reducable quartic), and they asked u 2 find the root, if 1 is imginary u are not required 2 find it, just rite not real root, or impossible. im not sure wot they would do if u found the imaginary root, but why would u bother. lol
4u stuff can be used in 3u, i.e with polynomials and graphing and intergration. but again imaginary number i would not use, because they dont deal with them.
usally they are specific in wot they want u 2 do in 3u, so the 4u students arnt at an advantage, same in 2u so the 3u students arnt at an advantage.