VCE Specialist 3/4 Question Thread!

[Stevensmay]

Ahhhh, I went back and did it on CAS, don't know how I got it wrong, do you guys have the "Plot differential equation" program on your CAS? Super useful.

I know the later software updates for the TI Nspire range bring the ability to graph slope fields.
The implementation isn't that great but is enough for most exam questions.

If anyone is interested, Re: Specialist Mathematics Resources
It is a very useful guide with lots of other tricks.

[e^1]

Hey everyone

If anyone could help, I don't understand what they mean by "dummy variable" in this question. Could someone explain what it is?

Thank you!

[lzxnl]

"Dummy variable" here refers to the fact that the name of the variable doesn't matter. I'll illustrate with an example.

Suppose you had some axes, the x and y axes in standard orientation. Now let's draw up y=sin x and we want the area bound between the graph, the x axis and the lines x=0 and x=pi/2. That's easy enough to work out. Does it matter if we replace "x" with "u"? No, it doesn't. The area is still the same. The integration procedure would replace ALL x's by u's, including in the differentials. The value of the integral is unchanged though, for reasons that are probably obvious by now.

This is what they mean by dummy variable.

[TrueTears]

lol dummy variable, why are they using econometrics/statistics terms

[LOLs99]

Hello I have a question from vcaa 2010 exam 2 Q4b) (ii).
If they ask for an exact value of the DEFINITE INTEGRAL in part i and this was a volume question. Would it be wrong if i put "units^3" after my answer?Because the VCAA solution does not have it. Thankyou

[Alwin]

Hello I have a question from vcaa 2010 exam 2 Q4b) (ii).
If they ask for an exact value of the DEFINITE INTEGRAL in part i and this was a volume question. Would it be wrong if i put "units^3" after my answer?Because the VCAA solution does not have it. Thankyou

Definite integral, eg just evaluate    then no units. In fact, if you put units you'll be marked down

But, if it's asking for a volume of area, eg   then you do need units! (it may just ask for the 'value of the ___' but personally I just always included units for these types of qs)

Hope the generalisation helps

[LOLs99]

Definite integral, eg just evaluate    then no units. In fact, if you put units you'll be marked down

But, if it's asking for a volume of area, eg   then you do need units! (it may just ask for the 'value of the ___' but personally I just always included units for these types of qs)

Hope the generalisation helps

Hi Alwin thanks for your response. But for that specific question, is it okay to put units? It is from vcaa 2010 Exam2 Q4b. It would be good if u can have a look for me. 

[b^3]

Hi Alwin thanks for your response. But for that specific question, is it okay to put units? It is from vcaa 2010 Exam2 Q4b. It would be good if u can have a look for me. 

Since you're asked to find the exact value of the definite integral, rather than 'find the volume', then you wouldn't need units (although in this case I don't think you'd be penalised if you put them).

EDIT: tbh, from memory they aren't really harsh on units in spesh or methods, things like physics and chem they are though. There's not really anything to lose by putting them in when appropriate though.

EDIT2: What I mean by EDIT1 still depends on the context though, if you were asked to find say, the number of foxes or number of months, then you'd need 6 foxes or 6 months as your units.

[LOLs99]

Since you're asked to find the exact value of the definite integral, rather than 'find the volume', then you wouldn't need units (although in this case I don't think you'd be penalised if you put them).

I write down as V= pi^2/2 (no units)- correct? Yeah i guess they won't but technically i need some units for volume though

[b^3]

I write down as V= pi^2/2 (no units)- correct? Yeah i guess they won't but technically i need some units for volume though

What I'm getting at is in part bii were you asked to find or were you asked to find ? (and yes they're equivalent, but they did ask for the value of the definite integral).

For integral questions like this, VCAA don't put units in the examiners report. I'd still put them in just in case (technically not wrong), but it's more for the case where say you're asked to find the number of months for something to happen. Then you'd need "X months" for your answer (where units matter, since it could be "X years" or "X days" e.t.c).

[LOLs99]

What I'm getting at is in part bii were you asked to find or were you asked to find ? (and yes they're equivalent, but they did ask for the value of the definite integral).

For integral questions like this, VCAA don't put units in the examiners report. I'd still put them in just in case (technically not wrong), but it's more for the case where say you're asked to find the number of months for something to happen. Then you'd need "X months" for your answer (where units matter, since it could be "X years" or "X days" e.t.c).

Oh haha i kept thinking they want volume because the part i mentioned volume. got confused. Alright, they just want the definite integral, so no unit required. Yeah I just dont want to throw away this kind of easy marks in  exam, not worth it. Thanks for helping b^3

[b^3]

Oh haha i kept thinking they want volume because the part i mentioned volume. got confused. Alright, they just want the definite integral, so no unit required. Yeah I just dont want to throw away this kind of easy marks in  exam, not worth it. Thanks for helping b^3

I think as Alwin said above, you don't have much to lose by putting the "cubed units" in there, while you have something to lose if you're meant to and you don't. It's probably best to just write "cubic units" there anyways, (like Alwin I used to always do it as well, they can't really take a mark off for putting it there but they can when you don't put it there and it's meant to be there).

[LOLs99]

I think as Alwin said above, you don't have much to lose by putting the "cubed units" in there, while you have something to lose if you're meant to and you don't. It's probably best to just write "cubic units" there anyways, (like Alwin I used to always do it as well, they can't really take a mark off for putting it there but they can when you don't put it there and it's meant to be there).

I will take that advice thanks Alwin and B^3

[~T]

I disagree with the answer the question for Neap 2010 exam 2, multiple choice 22. The question is attached below and the answer is D. I'm just checking if my thoughts are valid.

I feel like A and B cannot both be true. If v is only defined for then shouldn't acceleration only be defined for ? If yes, then A if false. If not, then A is true and thus B is false, as zero isn't negative. Obviously D is false anyway - as required - but I'm just wondering what your thoughts are. If it wasn't a multiple choice question, and the same restrictions were in place, would you consider acceleration to be defined at t=0?

[Aelru]

^ Not sure if I'm answering your actual question, but why not differentiate the expression as a function of t, then sub in t=0?

>
>sub in t=0,
>so A is true, and because t is either 0 or a positive number, acceleration is always negative due to the negative sign in the numerator(ie. B is true)

Then again, you might have tried it already, and I might have completely missed the gist of your question lol.