quick question about volumes (1 Viewer)

[messagebrd]

Does anyone know if revolutions about the line y=x is still in the syllabus?

And if it is... how do you approach these questions? They confuse the hell out of me.

 

[study-freak]

I've never seen questions asking volume of solid of revolution about y=x although I've seen hundreds of 4U volume questions. Hence I guess it isn't in the syllabus.

 

[wixxy2348]

Yeah it'd not in the syllabus, as far as I'm aware.

 

[clintmyster]

my teacher said theres an example of it in cambridge. Def not in syllabus tho

 

[annabackwards]

Oh, so those questions that my teacher gave me was for no reason >.>

 

[Aquawhite]

I assume that this is 4U integration and volumes since it's in here but I'm quite sure I've done volumes around the line y=x before... maybe I'm mistaken by what you mean.

 

[annabackwards]

I assume that this is 4U integration and volumes since it's in here but I'm quite sure I've done volumes around the line y=x before... maybe I'm mistaken by what you mean.

You probably have, i did but apparently we don't need to know it anymore ><"

 

[kwabon]

those took so much time to figure out, and once i came to know they werent in the syllabus,
i went high

 

[Aquawhite]

May I ask why people took so long to figure out y=x for volume of revolution? It isn't like it's all that hard... I must be thinking of something else if so many of you say you took a while to figure out how to work it.

 

[clintmyster]

haven't looked at them but do they require a variation to your usual shells/slicing?

 

[untouchablecuz]

they'll usually involve follow up questions where you prove a relationship or 2. from here you wood consider the line y=x a seperate axes. then you integrate from a certain point on the line to another point (using the proven relations), using normal methods. it usually helps to spin your paper so that the new y=x axis is in line with your sight.

 

[messagebrd]

we did it in school, so i assume it can be examined in school exams only. Glad to hear that it's not in the syllabus though, so it can't be examined in my HSC .

I've seen the Cambridge example though and i don't get it.

*praying it's not coming in my upcoming assessments*

 

[jet]

May I ask why people took so long to figure out y=x for volume of revolution? It isn't like it's all that hard... I must be thinking of something else if so many of you say you took a while to figure out how to work it.

You might be thinking of the volume from the revolution of y=x around the x- or y-axis. The OP means volumes of solids rotated about the line y=x.

IMO it can get tricky, but if you work step-by-step with a good, large well-labelled diagram, you should get there.

 

[Casper_18]

I think it is in the syllabus. Otherwise why would they put it in a hsc textbook??

 

[Dragonmaster262]

I think it is in the syllabus. Otherwise why would they put it in a hsc textbook??

The textbook might be out of date.

 

[kwabon]

I think it is in the syllabus. Otherwise why would they put it in a hsc textbook??

naah man, checked twice. saw nothing about rotating volumes about y=x.

 

[lolokay]

the textbook gives a lead in, and then it becomes a usual slicing question but with r and h instead of x and y. I think that type of question probably could be tested, as it doesn't really require any extra knowledge.

 

[GUSSSSSSSSSSSSS]

there is actually a question in a 2004 kings trial (i think it's kings at least lol) with a question like this

but as lolokay says, it just requires a bit of lead in work, and then all that's different is that ur not using x and y as variables

xD

 

[gurmies]

Yeah, it leads you in with a relationship as everyone has said, and you end up transposing it to the hr plane...it's not extremely difficult.