q4 biased toward 4 unit (1 Viewer)

[jennylim]

i actually did that one with no problem. i mean, i initially went "oh, sin^2x, must be 1/2(1-cos2x) before realising the substitution.

what a few of my friends had issues with was that one with tanx/2 = t...that's 3u maths, but in 4u terms. sort of like our 2u paper question 10a - it was 2u level maths, but a 3u person who was familiar with parametrics would have done it with more ease.

but really, what's stopping them doing that? they do need to differentiate good maths students from average ones, and of course the 4u people are going to do better - they must be better at maths, do more work and learn a lot more stuff. so i'm not too fussed.

 

[jarro_2783]

t = tan(x/2) is in our year 11 textbook. It's just a matter of remembering the formula.

The question was show that cosecx + cotx = cot(x/2)

If you remember your formulas you will remember that tanx = 2t/(1-t²), cosx = (1-t²)/(1+t²) and sinx = 2t/(1+t²)

Therefore cosecx = (1+t²)/2t and cotx = 1-t²/2t

so cosecx + cotx = (1+t² + 1-t²)/2t
= 2/2t
= 1/t
but t = tan(x/2)
1/t = 1/tan(x/2)
= cot(x/2)

not that hard.

 

[jennylim]

haha i didn't have issues with that (i'd done a similar question the day before so i'd learnt those things...thankfully!!!!) but a lot of other people were annoyed with it.

things i DID have issues with, tho, include part 3 of the projectiles question and pretty much all of q7. dammit.

 

[DRAGONZ]

^ hey Dragonz, u remember Felix back in yr 10?
he was there topping eng. ext. 1 i think, den left..
hehe

Hu? Felix Who?

ROFL.

Hu are we talking about?!

No. Seriously ... Hu are we talking about?!?

Why do you ask?

 

[boasboy]

yer that projectiles was 4u styles.. and i didnt get this question out.. i always thought sin^2x = 1/2(1-cos2x)

then i just got stuck there.

 

[haboozin]

yer that projectiles was 4u styles.. and i didnt get this question out.. i always thought sin^2x = 1/2(1-cos2x)

then i just got stuck there.

4u projectile??

theres no such thing. If there is, that wasnt 4unit projectile. THere is a similar Question like this one in 2003 - 3unit .... 4 marks Q 5 (or 4) ... same principles... if u cant do that - u cant do this.
the only 4u projectile i can think of is resistant projectile... which is basicly like vertical resistant motion but with x /y components (nothing new). Thats been in the hsc like once

 

[香港!]

LOL
nvm nvm hehehe

 

[Captain pi]

"All examples" includes the one on page 71 and in all 3 unit exams during the lifetime of the syllabus.

Hence the question in this year's 3 unit paper is a 4 unit question.

Incorrect. That phrase does not apply to that particular question. The example says "3U students should be able to solve [integrands] of the type 2cos²(x) and cos(x)·sin²(x)". It does not say the substitution must be given. The substitution must only be given in such questions as are "exemplified" on page 66.

It's a 3U question. Sorry, but teachers should teach 3U students this method. Ours did.

 

[koala_face]

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 this question practically led u through it, do this now find this...ofcourse they're bloody connected!

 

[volition]

Yes, I agree with you about this being a possible '4 unit' question, but I'm not really all too worried if it's gonna be an easy one like this anyway. I 'only' do 3unit, and I had no problems with this question at all.

 

[Dumsum]

I agree with justchillin. This question isn't not only 4u, it's not even 3u, it's 2u stuff. No substitution was necessary.