Maths Ext 2 Predictions/Thoughts (1 Viewer)

Trebla

Administrator
Administrator
Joined
Feb 16, 2005
Messages
8,118
Gender
Male
HSC
2006
is evaluating it and saying both are the same number not enough to prove it?
It's a circular argument. Prove that this trig result holds. Oh look, they happen to equal on a calculator therefore it is proven!
 

Siwel

Active Member
Joined
Aug 21, 2021
Messages
208
Gender
Male
HSC
2021
It's a circular argument. Prove that this trig result holds. Oh look, they happen to equal on a calculator therefore it is proven!
just thought it was kinda like the roots thing, if this polynomial can be tan3theta solve for theta then find the roots, then by plugging in the numbers to see which ones are the distinct roots.
 

Trebla

Administrator
Administrator
Joined
Feb 16, 2005
Messages
8,118
Gender
Male
HSC
2006
just thought it was kinda like the roots thing, if this polynomial can be tan3theta solve for theta then find the roots, then by plugging in the numbers to see which ones are the distinct roots.
But plugging in numbers to see what the exact trig value is lacks proper rigour, as you have effectively found the answer by direct computation rather than by proof. It is the same as claiming you have proven the exact value of something simply because the calculator says they're equal rather than by logical arguments.
 

uart

Member
Joined
Dec 10, 2008
Messages
66
Gender
Male
HSC
N/A
It looks dirty
But plugging in numbers to see what the exact trig value is lacks proper rigour,
Agreed that it looks dirty, but it's probably still valid.

The point is that it's not about proving that it is the correct answer, it's about proving that the other surd is not the correct answer.

It would of course be invalid to try to use a calculator to prove that it was equal, because whatever decimal precision you use, it can never prove equity to the surd. But in terms of simply ruling out the other solution (the only other feasible solution), then it's dirty but it's valid (in my opinion).
 

jyu

Member
Joined
Nov 14, 2005
Messages
623
Gender
Male
HSC
2006
It looks dirty

Agreed that it looks dirty, but it's probably still valid.

The point is that it's not about proving that it is the correct answer, it's about proving that the other surd is not the correct answer.

It would of course be invalid to try to use a calculator to prove that it was equal, because whatever decimal precision you use, it can never prove equity to the surd. But in terms of simply ruling out the other solution (the only other feasible solution), then it's dirty but it's valid (in my opinion).
pi/10 < pi/6, cos(pi/10) > sqrt(3)/2, easily shown that sqrt((5 - sqrt5)/8) < sqrt(3)/2 and sqrt((5 + sqrt5)/8) > sqrt(3)/2
 

notme123

Well-Known Member
Joined
Apr 14, 2020
Messages
1,002
Gender
Male
HSC
2021
HSC examiners have just posted the videos for HSC marking for the 2021 Extension 2 exam:

Q12, 15 - Jim Green (co-author of Maths in Focus Ext. 2):


Q11, 16 - Greg Wagner:


Q13, 14, MC - Piv Huot:


Videos for Ext1, Adv and Standard are also posted at https://www.youtube.com/channel/UCYWgSDiUVcDEorLosTqp8Bg/videos
it seems last years 4u cohort was very weak (just look at how well my mark aligned). question 16b looking back was not very difficult for a 4u paper and i was very surprised to hear only 10 people got 5/5. the discriminant should be a go-to when you hear 'two values' of something. i might sound like a hypocrite cuz i only got 2/5 in that question, resulting from wrong algebraic expansion after dot product, so thats where my marks stopped, but I had the discriminant and justification included in my answer. the turly hard questions in this test imo were 15cii, 15d, 16aiii and 16c.
 

idkkdi

Well-Known Member
Joined
Aug 2, 2019
Messages
2,454
Gender
Male
HSC
2021
it seems last years 4u cohort was very weak (just look at how well my mark aligned). question 16b looking back was not very difficult for a 4u paper and i was very surprised to hear only 10 people got 5/5. the discriminant should be a go-to when you hear 'two values' of something. i might sound like a hypocrite cuz i only got 2/5 in that question, resulting from wrong algebraic expansion after dot product, so thats where my marks stopped, but I had the discriminant and justification included in my answer. the turly hard questions in this test imo were 15cii, 15d, 16aiii and 16c.
definitely not weak. more so that 2020 HSC 4u difficulty was a huge bait for what was to be expected.
 

notme123

Well-Known Member
Joined
Apr 14, 2020
Messages
1,002
Gender
Male
HSC
2021
definitely not weak. more so that 2020 HSC 4u difficulty was a huge bait for what was to be expected.
maybe i was a bit harsh but ye i agree 2020 baited people. actually now that i think about it, i just think the marking centre was generous in the e4 cutoff. so maybe the cohort isnt weak per se but unprepared for the difficulty
 

jimmysmith560

Le Phénix Trilingue
Moderator
Joined
Aug 22, 2019
Messages
4,119
Location
Krak des Chevaliers
Gender
Male
HSC
2019
Uni Grad
2022
ECF stands for Error Carried Forward. It is an approach to marking in subjects like maths, where you will only be penalised for errors in your working for the previous part of a question, rather than also penalising the error in subsequent parts of the question, which naturally makes your working and answers in subsequent parts of the question incorrect.
 

synthesisFR

School Spirit Skit 1
Joined
Oct 28, 2022
Messages
4,236
Location
Getting deported
Gender
Male
HSC
2023
ECF stands for Error Carried Forward. It is an approach to marking in subjects like maths, where you will only be penalised for errors in your working for the previous part of a question, rather than also penalising the error in subsequent parts of the question, which naturally makes your working and answers in subsequent parts of the question incorrect.
ah makes sense does this also apply for stuff like chemistry?
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top