Sum of a geometric series help

[fatmongoose]

Hi, i have two questions that i need help with, if you can provide working out and an answer i will greatly appreciate it, thanks.

 

[Deleted member 4993]

Hi, i have two questions that i need help with, if you can provide working out and an answer i will greatly appreciate it, thanks.

What are your thoughts?

Please share your work with us ...even if you know it is wrong.

If you are stuck at the beginning tell us and we'll start with the definitions.

You need to read the rules of this forum. Please read the post titled "Read before Posting" at the following URL:

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[fatmongoose]

What are your thoughts?

Please share your work with us ...even if you know it is wrong.

If you are stuck at the beginning tell us and we'll start with the definitions.

You need to read the rules of this forum. Please read the post titled "Read before Posting" at the following URL:

http://www.freemathhelp.com/forum/announcement.php?f=33

Well i assume we are using the S = A/1-R formula
for the first questions its X/1-(NX^N+1)
which is as far as ive gotten.

The 2nd is even more confusing, the answer to both questions is B but im not sure how they got that answer.
Thanks

 

[Deleted member 4993]

Well i assume we are using the S = A/(1-R) formula ..... Those () are important - otherwise the meaning changes
for the first questions its X/1-(NX^N+1)
which is as far as ive gotten.

The 2nd is even more confusing, the answer to both questions is B but im not sure how they got that answer.
Thanks

That equation [S = A/(1-R)] is not directly applicable here......

S = x + 2x² +3x³ + 4x⁴.......

S*x =.....x² +2x³ + 3x⁴.......

S*(1-x) = x + x² + x³ + x⁴.......

Now you can apply the equation S = A/(1-R).......

 

[fatmongoose]

That equation [S = A/(1-R)] is not directly applicable here......

S = x + 2x² +3x³ + 4x⁴.......

S*x =.....x² +2x³ + 3x⁴.......

S*(1-x) = x + x² + x³ + x⁴.......

Now you can apply the equation S = A/(1-R).......

So would it be s(1-x) = X/(1-x)
then if we divide both sides by (1-x) we get s = x/(1-x)(1-x) which isnt the correct answer.

what would be the name of these type of questions, when i google geometric series formulas i get simpler questions with series that involve numbers only.
Thanks in advance

 

[fatmongoose]

That equation [S = A/(1-R)] is not directly applicable here......

S = x + 2x² +3x³ + 4x⁴.......

S*x =.....x² +2x³ + 3x⁴.......

S*(1-x) = x + x² + x³ + x⁴.......

Now you can apply the equation S = A/(1-R).......

oh wait i got it, sorry i put the sign the wrong way. i understood the first question, now the 2nd question i will try using the same method. thank you