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October 07, 2025, 05:53:18 am
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Author Topic: dejan91's questions  (Read 16940 times)  Share 

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Over9000

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Re: dejan91's questions
« Reply #30 on: April 11, 2009, 12:11:45 am »
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First reaarange so that x and y are seperated



divide both sides by 3 to have coefficient as 1

Complete the square



and

Now:
......1
...............2
However lets be sneaky and sub in y=x+1 and as we have worked them out





and

therefore y=1 and
So points of intersection are (0,1) and

you can check, by subbing y=x+1 into equation 2 if u want
« Last Edit: April 11, 2009, 12:17:48 am by Over9000 »
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TrueTears

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Re: dejan91's questions
« Reply #31 on: April 11, 2009, 12:14:39 am »
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^^^^^^^^ SO F***KING PRO, I was stuck on this Q for like ages. pro pro legendary man.
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dejan91

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Re: dejan91's questions
« Reply #32 on: April 11, 2009, 01:49:44 am »
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Thanks heaps Over9000 :)


Might I add, explanation was A++
« Last Edit: April 11, 2009, 01:57:08 am by dejan91 »
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Over9000

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Re: dejan91's questions
« Reply #33 on: April 11, 2009, 01:54:58 am »
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Quote from: dejan91 on April 11, 2009, 01:49:44 am
Thanks heaps Over900 :)


Might I add, explanation was A++
No probs, glad to help  ;)
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dcc

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Re: dejan91's questions
« Reply #34 on: April 11, 2009, 11:00:15 am »
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Quote from: dekoyl on March 29, 2009, 09:48:37 pm
That was using the cross product as the cross product of two vectors is perpendicular to the two vectors. However it's not in the specialist course so unfortunately you can't use it in the exam. :P

Incorrect.  Any maths assessor worth their weight in salt will know and understand the cross product (god, even the physics assessors would).
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Mao

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Re: dejan91's questions
« Reply #35 on: April 11, 2009, 06:22:26 pm »
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Quote from: dcc on April 11, 2009, 11:00:15 am
Quote from: dekoyl on March 29, 2009, 09:48:37 pm
That was using the cross product as the cross product of two vectors is perpendicular to the two vectors. However it's not in the specialist course so unfortunately you can't use it in the exam. :P

Incorrect.  Any maths assessor worth their weight in salt will know and understand the cross product (god, even the physics assessors would).

I should add that, unless specified by the question, any method that is logically coherent and rigorous will be marked as correct. (But they design the questions with this in mind, so that CAS kids and UMEP/MUEP kids aren't at an advantage)

However, personally I would stay on the safe side and stay within the syllabus.
« Last Edit: April 11, 2009, 06:24:00 pm by Mao »
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dekoyl

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Re: dejan91's questions
« Reply #36 on: April 11, 2009, 08:15:10 pm »
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Quote from: dcc on April 11, 2009, 11:00:15 am
Quote from: dekoyl on March 29, 2009, 09:48:37 pm
That was using the cross product as the cross product of two vectors is perpendicular to the two vectors. However it's not in the specialist course so unfortunately you can't use it in the exam. :P

Incorrect.  Any maths assessor worth their weight in salt will know and understand the cross product (god, even the physics assessors would).
Cool. I didn't know that. I made a big assumption then as I asked my teacher if the cross product could be used and he said no.
I stand corrected.
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Re: dejan91's questions
« Reply #37 on: April 11, 2009, 08:19:48 pm »
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Quote from: dekoyl on April 11, 2009, 08:15:10 pm
Cool. I didn't know that. I made a big assumption then as I asked my teacher if the cross product could be used and he said no.
I stand corrected.

If your teacher says that the cross product doesn't exist, then you shouldn't use it when you are doing maths for your teacher.  (Its a parallel of price discrimination.  Maths discrimination: doing maths based on who will be reading it)
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ed_saifa

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Re: dejan91's questions
« Reply #38 on: April 11, 2009, 08:25:43 pm »
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When using maths that isn't on the syllabus, you won't get working marks if you get the answer wrong, or so i've been told.
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dejan91

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Re: dejan91's questions
« Reply #39 on: April 13, 2009, 09:39:16 pm »
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EDIT: Sorry, accidently clicked post before i finished.
Question was:  Solve for x where :


            





Let


and

I used this but only got one solution out of a possibl four. What did I do wrong? Or haven't I gone far enough?
« Last Edit: April 13, 2009, 09:52:16 pm by dejan91 »
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TrueTears

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Re: dejan91's questions
« Reply #40 on: April 13, 2009, 09:45:03 pm »
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Null factor law or

Can you do it from here?
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dejan91

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Re: dejan91's questions
« Reply #41 on: April 13, 2009, 09:51:42 pm »
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Cool thanks TrueTears, do you know if my way was wrong?
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Re: dejan91's questions
« Reply #42 on: April 13, 2009, 09:53:44 pm »
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Your mistake was that you cancelled out a possible solution when you simplified by cancelling out the cos(2x)
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dejan91

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Re: dejan91's questions
« Reply #43 on: April 13, 2009, 09:56:06 pm »
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Hmm I see. Ok then thanks for pointing that out.
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Re: dejan91's questions
« Reply #44 on: April 13, 2009, 10:00:27 pm »
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Say you have sinxcosx = cosx

if you cancel cosx from both sides, you are in fact losing a solution

this is the same thing as saying



you wouldn't cancel a x on both sides, because it will lose a solution, so that's why you move to the LHS and do null factor.
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