Malcolm's big Help me with Maths thread (soon to be big) Watch

Fafnir
Badges: 1
Rep:
?
#21
Report 11 years ago
#21
(Original post by generalebriety)
Spoiler:
Show
Isn't that where the GP formula comes from?
Spoiler:
Show
Sort of, but it's in heavy disguise - at least the way it's presented by Edexcel. Their proof takes the series S = \sum_{k=0}^{n}ar^{k} and subtracts rS to get a closed form for S, rather than explicitly expressing each term in S as a term that will cancel with other terms in S as in FP1 (where the method is explicitly covered).

I was thinking of using \frac{n^{2}}{(1+n^{2})^{r}} = \frac{1}{(1+n^{2})^{r-1}} - \frac{1}{(1+n^{2})^{r}} - it looks faster and less painful than plugging a = \frac{n^{2}}{1+n^{2}}, r = \frac{1}{1+n^{2}} into the GP formula, and relatively easy to spot.
0
reply
generalebriety
Badges: 14
Rep:
?
#22
Report 11 years ago
#22
(Original post by Fafnir)
Spoiler:
Show
Sort of, but it's in heavy disguise - at least the way it's presented by Edexcel. Their proof takes the series S = \sum_{k=0}^{n}ar^{k} and subtracts rS to get a closed form for S, rather than explicitly expressing each term in S as a term that will cancel with other terms in S as in FP1 (where the method is explicitly covered).

I was thinking of using \frac{n^{2}}{(1+n^{2})^{r}} = \frac{1}{(1+n^{2})^{r-1}} - \frac{1}{(1+n^{2})^{r}} - it looks faster and less painful than plugging a = \frac{n^{2}}{1+n^{2}}, r = \frac{1}{1+n^{2}} into the GP formula, and relatively easy to spot.
Hadn't thought of that. Not bad.
0
reply
generalebriety
Badges: 14
Rep:
?
#23
Report 11 years ago
#23
(Original post by Square)
Right heres my working:

\mathrm{S_n}=\frac{a(1-r^n)}{1-r}

Subbing in:

=\frac{(\frac{b^2}{1+b^2})(1-\frac{1}{(1+b^2)^n})}{1- \frac{1}{1+b^2}}

Simplify:

\frac{b^2(1 - \frac{1}{(1+b^2)^n})}{b^2}

Cancel out b^2

1-\frac{1}{(1+b^2)^n}

I still don't think this is right.

EDIT: Hmm, LaTeX doesn't seem to like all my fractions, if you know a tidier way to do the algebra please let me know.
Looks right to me.
0
reply
Square
Badges: 12
Rep:
?
#24
Report Thread starter 11 years ago
#24
Posted my working at the bottom of the last page, must've got hidden by the creation of a new page :p:.

As I said I'm still not sure if it is right. Have found another similar question which I am gonna try and work through now.

Why can't everything just be calculus and vectors
0
reply
Square
Badges: 12
Rep:
?
#25
Report Thread starter 11 years ago
#25
(Original post by generalebriety)
Looks right to me.
Righty, the whole rewriting it using different letters seems to have made the penny drop then :p: I think I was just getting confused with the r's and a's and thus my algebra was just turning out absolutely horrible.

Will no doubt find osmething else troubling me later on so watch this space!

Cheers for the help.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • University of Derby
    Postgraduate and Professional Open Evening - Derby Campus Postgraduate
    Tue, 22 Jan '19
  • University of the West of England, Bristol
    Undergraduate Open Afternoon - Frenchay Campus Undergraduate
    Wed, 23 Jan '19
  • University of East London
    Postgraduate Open Evening Postgraduate
    Wed, 23 Jan '19

Brexit: Given the chance now, would you vote leave or remain?

Remain (1528)
79.29%
Leave (399)
20.71%

Watched Threads

View All