# Arithmetic Series

• Jun 19th 2013, 06:59 PM
Espionage
Arithmetic Series
The terms -2, 1+2k, 4+4k... form an arithmetic sequence. If the sum of the first ten terms is a+bk then give the value of a-b.

I got up to finding the common difference (2k+3). I don't know what to do after.
• Jun 19th 2013, 07:56 PM
mpx86
Re: Arithmetic Series
sum upto 10 terms will be of the form of c+dk
acc. to question S10=a+bk
can u calculate the value of a and b??
• Jun 20th 2013, 05:35 AM
ibdutt
Re: Arithmetic Series
firstly the the three ters given are not in ap because [( 4+4k) - ( 1 + 2k)] is not equal to [ ( 1+2k)-(-2)]
• Jun 20th 2013, 05:56 AM
Plato
Re: Arithmetic Series
Quote:

Originally Posted by ibdutt
firstly the the three ters given are not in ap because [( 4+4k) - ( 1 + 2k)] is not equal to [ ( 1+2k)-(-2)]

What do you mean? \$\displaystyle (4+4k)-(1+2k)=3+2k=(1+2k)-(-2)\$
• Jun 23rd 2013, 08:15 PM
ibdutt
Re: Arithmetic Series
I regret this post is wrong the given terms are in AP with common difference 2k+3. But with three variables a,b and k we need to have some more information to resolve the solution.
• Jun 23rd 2013, 09:01 PM
topsquark
Re: Arithmetic Series
Okay, let me try this again. Your sum will have a k in it. After all, we are given that the sum is of the form a + bk...

-Dan