Abbreviations.com Convert.net Definitions.net Quotes.net Synonyms.net USZip.net References.net
Bookmark & Share
 
Synonyms.net
Search for Synonyms:     
Browse Alphabetically:
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z #
 random synonym 
Personalize Yedda, (And make Danny Happy)
People ask & answer about almost everything. Tell us what you're interested in... So we can personalize Yedda especially for you
I'm interested in:
Save
Cancel

The sum of the first five terms of an arithmetic ...

The sum of the first five terms of an arithmetic sequence is 40 and the sum of the first ten terms is 155. Find an explicit formula for the nth term of the sequence.


Answer this question
Share Send to a friend Watch Report
 
 

2 Posted Answers
Order by

 
8452 answers
4552 helpful answers

Love is the battery of life....

Hi, ------ S(5)= 40 = (a1+a5)*5/2= (2a1+4d)5a1+10d ---- 8=a1+2d ----- S(10)= 155 = (a1+a10)*10/2= (a1+a1+9d)*5 = 10a1+45d -------- 31=2a1+9d From the 1st equation: a1=8-2d install in the 2nd equation: 31=2(8-2d)+9d ----- 31=16-4d+9d ---- 15=5d d=3 and a1=2 ------- a9=a1+8d ------ a9=2+3*8=26 -------- Best regards,

Posted 2009-05-26T05:58:37Z
Helpful?(1)
Rated as Best Answer
 
Ian
316 answers
67 helpful answers

a + (a + d) + (a + 2d) + (a + 3d) + (a + 4d)

(a+5d) + (a+6d) + (a+7d) + (a+8d) + (a+9d)

5a + 10d = 40                                         (a)

10a + 45d = 155                                      (b)

10a + 20d = 80                                      2 x(a)

25d = 75                                           (b) - 2 x(a)

d = 3

a + 2d = 8 = a + 6                           from (a)/5

a = 2

Sequence is 2, 5, 8, etc.

nth term is a + (n -1)d = 2 + 3(n -1) = 3n -1

Every term is a multiple of three reduced by 1

Regards - Ian

 

 

 


 
Posted 2009-05-30T22:28:37Z
Ian was invited by Yedda to answer this question.

Helpful?(0)
Rated #2 out of 2

Sign in to participate

Got an answer for marewags? Would you like to comment on the posted answers, or vote for the one which you think is the best?

Sign up for a free account, or sign in (if you're already a member).

Feed - Subscribe to changes to this Q&A Blog
ADVERTISEMENT
Synonyms.net Q&A is powered by Yedda an AOL Company
Copyright © 2006-2009, Yedda Inc. and respective copyright owners
Home |  Add New Abbreviation |  Your List |  Tools |  Become an Editor |  Tell a Friend |  Links |  Awards |  Testimonials |  Press |  News |  APIs new! |  About
Copyright ©2004-2007 STANDS4 LLC. All rights reserved.  Terms of Use  |  Privacy Policy  |  Contact Us