2013 CSSA Mathematics Thoughts? (1 Viewer)

[bedpotato]

Is it y>1/2 or y>=1/2???

y > 1/2

 

[coyney]

Hate to ruin people's days further, but Wagig pointed it out to me that the second 12hrs would be the next day... and so the sum would be 2x(that thing) - 12.

Made the same mistake :L

I'm pretty sure you don't take away 12, because you don't count the 12 for 12 am as the first ring... 1am + 2am + 3am + 4 + 5 +6 +7 +8 +9 +10 +11 +12pm + 1pm + ....... + 12 am
So i'm sure its 156

 

[Triage]

y > 1/2

Or equal to. Lol why would it be strictly greater than? What part of the solution excluded it equaling 1/2?

 

[bedpotato]

Or equal to. Lol why would it be strictly greater than? What part of the solution excluded it equaling 1/2?

| r | > 1.
That's what I used to solve for y.
What did you do?

 

[Triage]

| r | > 1. Sorry, not < .
That's what I used to solve for y, where r = y^2/(y-1)^2.
What did you do?

I solved for infinite sum and did the opposite in the end
So -1<y^2/(y-1)^2 < 1

The -1 got eliminated because it has no real solutions.

 

[dunjaaa]

The question was: for what values of y does this series does not have an infinite sum, I solved for r>1 and r<-1. r<-1 gave no solution and r>1 gave a solution of y>1/2. I think I got this question wrong since my friend pointed out to me that since the question implies that for this series to not have a infinite sum means that it has a limiting sum which meant you had to solve for r<1 and r>-1. Idk if thats correct or not but it sounds right. Lost 1 mark if he is right.

 

[bedpotato]

The question was: for what values of y does this series does not have an infinite sum, I solved for r>1 and r<-1. r<-1 gave no solution and r>1 gave a solution of y>1/2. I think I got this question wrong since my friend pointed out to me that since the question implies that for this series to not have a infinite sum means that it has a limiting sum which meant you had to solve for r<1 and r>-1. Idk if thats correct or not but it sounds right. Lost 1 mark if he is right.

Yeah, I understand where you're coming from. But a limiting sum IS an infinite sum, it just has a limit. Lol, this is confusing me.

 

[dunjaaa]

Thats what I thought as well...

 

[RealiseNothing]

The question was: for what values of y does this series does not have an infinite sum, I solved for r>1 and r<-1. r<-1 gave no solution and r>1 gave a solution of y>1/2. I think I got this question wrong since my friend pointed out to me that since the question implies that for this series to not have a infinite sum means that it has a limiting sum which meant you had to solve for r<1 and r>-1. Idk if thats correct or not but it sounds right. Lost 1 mark if he is right.

Your friend is wrong.

 

[RealiseNothing]

The question was: for what values of y does this series does not have an infinite sum, I solved for r>1 and r<-1. r<-1 gave no solution and r>1 gave a solution of y>1/2. I think I got this question wrong since my friend pointed out to me that since the question implies that for this series to not have a infinite sum means that it has a limiting sum which meant you had to solve for r<1 and r>-1. Idk if thats correct or not but it sounds right. Lost 1 mark if he is right.

Also you are meant to solve for

 

[iBibah]

Yeah, I understand where you're coming from. But a limiting sum IS an infinite sum, it just has a limit. Lol, this is confusing me.

A limiting sum isn't an infinite sum. A limiting sum is a sum with infinite terms, however the sum of those terms is not infinity.

An infinite sum means the sum of the terms is infinite, it doesn't imply it has infinite terms (it DOES have infinite terms, but the name 'infinite sum' isn't so for that reason.

So while both limiting and infinite sums have infinite terms, they dont both have a sum that is infinity.

 

[wagig]

If an infinite sum exists, that means there is a finite sum as the number of terms approaches infinity right?

 

[bedpotato]

Also you are meant to solve for

How come?

A limiting sum isn't an infinite sum. A limiting sum is a sum with infinite terms, however the sum of those terms is not infinity.

An infinite sum means the sum of the terms is infinite, it doesn't imply it has infinite terms (it DOES have infinite terms, but the name 'infinite sum' isn't so for that reason.

So while both limiting and infinite sums have infinite terms, they dont both have a sum that is infinity.

Oh okay. Thanks.

 

[RealiseNothing]

A limiting sum isn't an infinite sum. A limiting sum is a sum with infinite terms, however the sum of those terms is not infinity.

An infinite sum means the sum of the terms is infinite, it doesn't imply it has infinite terms (it DOES have infinite terms, but the name 'infinite sum' isn't so for that reason.

So while both limiting and infinite sums have infinite terms, they dont both have a sum that is infinity.

No an infinite sum is just a sum of infinite terms.

 

[RealiseNothing]

How come?

If r=1 the sum still tends to infinity.

 

[iBibah]

Also you are meant to solve for

How is solving for that going to determine the value for which it is NOT an infinite sum?

 

[dunjaaa]

Isnt it r>1

 

[Triage]

Also you are meant to solve for

Oh yeah that's how I got it. Lol I was wondering how I got it then i realised, if a limiting sum is strictly less, then not a limiting sum must be equal to or greater than

 

[Triage]

When will you people realise. An infinite sum, is a sum (defined) as n goes to infinite. Lol how is that even a question. An infinite sum. Not an infinite infinite

 

[wagig]

When will you people realise. An infinite sum, is a sum (defined) as n goes to infinite. Lol how is that even a question. An infinite sum. Not an infinite infinite

This^ (i hope haha)