User Name Remember Me? Password

 Algebra Pre-Algebra and Basic Algebra Math Forum

April 29th, 2015, 02:15 PM   #1
Senior Member

Joined: Jan 2015
From: USA

Posts: 107
Thanks: 2

Very challenging sequence 1

Hi! Does anyone know how to solve this problem! Thanx
Attached Images Sequence 1.jpg (30.2 KB, 11 views) April 29th, 2015, 03:16 PM #2 Math Team   Joined: Nov 2014 From: Australia Posts: 689 Thanks: 244 The partial sum of a geometric series from the first term to the $n$th term is $S_n = \dfrac{a(r^n - 1)}{r - 1}$ Where $a$ is the first term and $r$ is the common ratio. In your question, you would end up with the formulae $\dfrac{a(r^x - 1)}{r - 1} = 200$ and $\dfrac{a(r^{zx} - 1)}{r - 1} = 16400$ Now solve for $a$ and $r$. Thanks from matisolla April 29th, 2015, 03:50 PM #3 Global Moderator   Joined: Oct 2008 From: London, Ontario, Canada - The Forest City Posts: 7,958 Thanks: 1146 Math Focus: Elementary mathematics and beyond I believe that's "2x", not "zx". matisolla, what have you tried? April 29th, 2015, 04:21 PM   #4
Senior Member

Joined: Jan 2015
From: USA

Posts: 107
Thanks: 2

Quote:
 Originally Posted by greg1313 I believe that's "2x", not "zx". matisolla, what have you tried?

Indeed my friend, it is 2X. Sorry for the resemblance in of z and 2 in my afwul calligraphy! I attach a picture of my progress so far. I dont know how to continue from there. I would appreciate your help, since you always help me in this page! Attached Images 11198943_10153306495409700_2115045634_n.jpg (52.5 KB, 6 views) April 29th, 2015, 04:35 PM #5 Global Moderator   Joined: Oct 2008 From: London, Ontario, Canada - The Forest City Posts: 7,958 Thanks: 1146 Math Focus: Elementary mathematics and beyond $\displaystyle \frac{a(r^x-1)}{r-1}=200\Rightarrow r-1=\frac{a(r^x-1)}{200}$ $\displaystyle \frac{a(r^{2x}-1)}{r-1}=\frac{200a(r^{2x}-1)}{a(r^x-1)}=16400$ $\displaystyle \frac{r^{2x}-1}{r^x-1}=82$ $\displaystyle \frac{(r^x-1)(r^x+1)}{r^x-1}=82$ $\displaystyle r^x+1=82$ $\displaystyle r^x=81$ $\displaystyle a=5,r=3\text{ (with }x=4)\text{ or }a=20,r=9\text{ (with }x=2).$ Your handwriting is difficult to read. Type out your posts! Tags challenging, sequence Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Threads Thread Thread Starter Forum Replies Last Post matisolla Geometry 2 February 12th, 2015 02:31 PM matisolla Linear Algebra 2 February 11th, 2015 06:08 AM davedave Calculus 28 November 12th, 2012 02:36 AM matemagia Algebra 2 August 22nd, 2012 03:58 AM huu3y2 Calculus 1 April 22nd, 2011 07:12 PM

 Contact - Home - Forums - Cryptocurrency Forum - Top

Copyright © 2019 My Math Forum. All rights reserved.      