q4 biased toward 4 unit (1 Viewer)

[jarro_2783]

I did four unit and according to what our teacher told us, the integral in question 4 was biased toward four unit students. Our teacher said that in three unit you aren't expected to work out the substitution and that it would be given to you, but in four unit you are. So I looked at it and straight away thought u = sinx and then thought the 3 unit people are going to be screwed.
What does everyone else think?

 

[rama_v]

Yeah, I didnt think they woudl actually put that in the HSC. I only do 3 unit, but luckily we use the Fitzpatrik book at school and it has questions that are like the ones we got today, and they dont give substitutions in the book, so it wasn't a hassle for our class at least.

 

[tim_dawborn]

i did it a different way

noted that (d/dx)sin^3x = 3sin^2xcosx and used that

 

[PiGMAN]

have a cry. I'm sure it's in the 3unit syllabus.

 

[haboozin]

well thats what this year was all about...
not really go in depth with any part of the course but just have questions which put people off.. (so the truely good people still do well - but the ppl that just cram and dont understand the course fail misterably)

there's even 2unit tests that they put integration without substitution..

 

[Captain Gh3y]

*swears loudly*

Wow, that question is actually REALLY EASY if you use u = sinx.

It is in the 3 unit syllabus, we're expected to be able to figure out what one would differentiate in order to arrive at that.

 

[PiGMAN]

and I object to the anti-4unit sentiment in this forum. We do more work than you, thus our marks are better, period.

 

[Napoleon]

i concur

Period!...

 

[_dhj_]

Yeah when I saw the question I was like.. "huh.. i didn't know this was in the 3u syllabus". But of course any question is gonna be biased towards 4u, as we do far more study and tend to be the people who are better at maths

 

[kyu_chan]

I did four unit and according to what our teacher told us, the integral in question 4 was biased toward four unit students. Our teacher said that in three unit you aren't expected to work out the substitution and that it would be given to you, but in four unit you are. So I looked at it and straight away thought u = sinx and then thought the 3 unit people are going to be screwed.
What does everyone else think?

I'm a 3Uniter... I got to that and went "what the f*ck?"... but managed to play around with it and did substitution (i'm okay at substitution)... so managed.

 

[physician]

Yeh I thought of using 'u' ... but for some reason i didnt, but i think i sort of worked out something probably enough to get me at least 1 mark...who knows!...

I don't really think it was a 4unit question I've see a similar question in a previous paper I think I even called the advice line about it... but funny enough i forgot how to solve it in the exam.

hehe it looks like the same argument raised in the 2unit maths section is being raised again here... But No! I dont think there is an issue here! (and no, i dont do 4 unit)...

 

[sambo_rambo]

I don't know if this is really wrong but i used the sin^2(x) identity thing and then expanded. I got a cos^2(2x) and then I used the same thing again but the cos^2(x) identity thing. Does that make sense?

 

[justchillin]

Omg dude dont be soo ignorant...I want u to find d/dx (sinx)^3...its called chain rule u learnt in 2 unit...there was no bias, so dont be bitchy

 

[sambo_rambo]

What's component B?

 

[香港!]

You don't need a "substitution" for that question..
int. cosxsin²x dx=int. sin²x d(sinx)=sin³x\3+C
NO substitution required

 

[tim_dawborn]

Omg dude dont be soo ignorant...I want u to find d/dx (sinx)^3...its called chain rule u learnt in 2 unit...there was no bias, so dont be bitchy

i agree !!

 

[noah]

you dont need the substitution its a very basic 3u concept that cos x is the derivative of sin x. it is only a matter of applying the function of a function rule in reverse.

 

[chin music]

I looked at that question for fuckn ages and had no fuckn idea what to do. I thought of using a substitution but i was all but sure they had to give u the substitution in 3 unit. But.. I guess the paper proved me wrong.

 

[mattplaysguitar]

im just a 3 uniter and i looked at it and knew straight away. our teacher gave us like 20 questions on integrating those types of ones so i knew it well. in the 3 unit excel formula book it actuallly has those in it and it states that 3 unit students are xpected to realise that its the derivative of the sin^3 x and then abit of twisting around with the 1/3 bit. all in all its not biased towards 4 unit i dont think, 3unit people should have known it

 

[DRAGONZ]

Omg dude dont be soo ignorant...I want u to find d/dx (sinx)^3...its called chain rule u learnt in 2 unit...there was no bias, so dont be bitchy

For someone who got 83/84 in the exam today, you should know the correct name of the rule you applied there

I dare you to use THE CHAIN RULE as you called it on the integral of (cosx)(sinx)^2

you dont need the substitution its a very basic 3u concept that cos x is the derivative of sin x. it is only a matter of applying the function of a function rule in reverse.

noah is aware of the procedure

The REVERSE chain rule, justchillin. REVERSE!!