how was amath paper 2?

qdtimes2 SG

i spelt inflexion and inflexation! will they be lenient?

forum-er93 SG

lol. the most -1 lor.
and a1 is like around 80%. not as high as 85%

ViewtyKU990 SG

I think most of you still dun realise that you lost 2 marks.

I will bet my underwear that most people did d2y/dx2 =0 and think it is sufficient proof that it is a point of inflexion. Unfortunately it is not.

Visualise the graph of y = x^4

dy/dx = 4x^3

when dy/dx = 0

4x^3=0

x=0

d2y/dx2 = 12x^2

d2y/dx2 = 12(0)^2

d2y/dx2 = 0

Now look at your mental picture of y = x^4, is the turning point a point of inflexion?

To prove point of inflexion, you need to use the outline method.

it is for sure inflexion, and is and cubic curve not a X^4 curve btw..

x | 0.99 | 1 | 1.01

dy/dx | >0 | 0 | >0

sketch | / | _ | /

Mikethm SG

lol. the most -1 lor.
and a1 is like around 80%. not as high as 85%

Last year, I had 2 students who reported a score of 86% after checking their answers against answers I provided. They both got A2.

This year's paper is only barely just a teensy bit harder... So 85% is a good guage.

Considering more than a third my students lost 25-30 marks this year... I would hope that 80% is the cut off for A1 but I wouldn't hold my breath.

Mikethm SG

it is for sure inflexion, and is and cubic curve not a X^4 curve btw..

x | 0.99 | 1 | 1.01

dy/dx | >0 | 0 | >0

sketch | / | _ | /

I know and you did it the correct way congratulations.

I was simply using the x^4 curve to illustrate why d2y/dx2 =0 does not prove that the turning point is a point of inflexion.

ViewtyKU990 SG

oh i see.. hahas.. but i simply died out at the binomial question, i used 1 hour plus to do that question and yet i still get the wrong answer

Mikethm SG

oh i see.. hahas.. but i simply died out at the binomial question, i used 1 hour plus to do that question and yet i still get the wrong answer

That does not surprise me. Because the night before, I asked my students to do this question...

And half still got the binomial question wrong. And I dun blame them... coz when I was preparing the model answers for them to estimate their losses... the binomial question took me 15mins to do even thought I knew exactly how it was going to proceed.

ViewtyKU990 SG

i totally missed out the point whereby they didnt give us a x^1 term for a + bx^2

HyuugaNeji SG

still remember i can do all the questions in add maths and e maths paper 1 and 2. Like 4 x 100/100 if everything goes smoothly.

Took a look at last year (2008) add math's paper and holy, the geometry question was HARD. Took me a long time to solve it.

ViewtyKU990 SG

hmmm i lost a total of 12 marks for a maths now..

e maths a few, but i 4got..

hmm i prefer last year paper, i feel that it is easier. how sad that today's plane geometry didnt kill much D:

tangent secant, midpoint, intersecting chord theorem all didnt come out D:

qdtimes2 SG

Last year, I had 2 students who reported a score of 86% after checking their answers against answers I provided. They both got A2.

This year's paper is only barely just a teensy bit harder... So 85% is a good guage.

Considering more than a third my students lost 25-30 marks this year... I would hope that 80% is the cut off for A1 but I wouldn't hold my breath.

OMG! So high! just like Emath, if we make just a few careless mistakes, and .....

i wonder if the cut-off points of other subjects like physics, chemistry, combined humanities, POA are this high too.

zeahway SG

-deleted

qdtimes2 SG

some other people cannot do the binomial expansion but i worse... cannot do plane geometry. Why can't I see that the congruent triangles have common sides =.=

My eyes have been playing fatal tricks on me in letter writing, comprehension and now this. Hais... I better not had any careless mistakes in paper 2.

Dejomel SG

Visualise the graph of y = x^4

dy/dx = 4x^3

when dy/dx = 0

4x^3=0

x=0

d2y/dx2 = 12x^2

d2y/dx2 = 12(0)^2

d2y/dx2 = 0

Now look at your mental picture of y = x^4, is the turning point a point of inflexion?

To prove point of inflexion, you need to use the outline method.

Yes, I did that.

May I assume I got the full 11 marks?

I lost 14 marks from blank questions, but I am pretty confident of getting 86/100.

In fact I NEED the 86/100 to score 81% overall.

Dejomel SG

That does not surprise me. Because the night before, I asked my students to do this question...

Sorry but may I ask you something? I wanted a professional's advice on this.

Considering that most of the 'top students' from 'top schools' like ACS(I), RI etc. are in the IB programme, shouldn't the bell curve be less harsh than >85% for an A1?

I understand if pure sciences require more than 85% for an A1, but for mathematics I always thought 80% for an A1 was more than enough.

Mikethm SG

Sorry but may I ask you something? I wanted a professional's advice on this.

Considering that most of the 'top students' from 'top schools' like ACS(I), RI etc. are in the IB programme, shouldn't the bell curve be less harsh than >85% for an A1?

I understand if pure sciences require more than 85% for an A1, but for mathematics I always thought 80% for an A1 was more than enough.

1st, I am not a professional. My interest in the score required was because got one year I got too many B3s.

There are still schools like SCGS, Victoria, Cedar, SJI (1/2 IB, 1/2 O), CHIJ St Nicholas etc etc you know? These schools have 80-90++% distinction ( defined as A1/A2) rates...

On the other hand, my students may have overestimated their scores? But I don't think that is likely as this year's 9 out of 11 students report losses of <33 marks (aka 82%). My average distinction rate is 70-80%. So what they feedback to me make sense as if we assume A2 is around 80%, I will get 82% distinctions.

And if A2 is 80%, A1 should be around 85% no?

Seowlah SG

Can post the binomial question here to see how difficult is it ?

qdtimes2 SG

5i) Write down the first three terms in the expansion, in ascending powers of x, of

(2 - x/4)^n , where n is a positive integer greater than 2. (3m)

The first two terms in the expansion, in ascending powers of x, of (1 + x)(2 - x/4)^n are

a + bx^2 , where a and b are constants.

ii) Find the value of n. (3m)

iii) Hence find the value of a and of b. (3m)

Seowlah SG

5i) Write down the first three terms in the expansion, in ascending powers of x, of

(2 - x/4)^n , where n is a positive integer greater than 2. (3m)

The first two terms in the expansion, in ascending powers of x, of (1 + x)(2 - x/4)^n are

a + bx^2 , where a and b are constants.

ii) Find the value of n. (3m)

iii) Hence find the value of a and of b. (3m)

You might have probably forgotten to type "The first two-non-zero terms are a + bx^2".

The trick to this question is to expand (1 + x)(2 - x/4)^n as usual and equate the x term to 0x as the first two non-zero terms are a + bx^2.

In fact the expansion should be a + 0x + bx^2 but the question is tricky and the question only says the first two non-zero terms are a + bx^2.

forum-er93 SG

VS prelim came out something similar.
just equate the coefficient of X to 0.

and alot of people do not know how to expand nCr.

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