# Arthimetic Series 2

• Feb 25th 2013, 07:48 AM
Mathnood768
Arthimetic Series 2
1. The first three terms of an arithmetic sequence are given by x, (2x-5), 8.6.

Determine the first term and the common difference.

I know that d = t2 - 1 = t3 - t2

So, (2x-5)-(x) = 8.6 - (2x-5) (Trying to solve for difference)

x - 5 = 3.6 - 2x

-5 = 3.6 - x

-5-3.6 = - x

x = 8.6

x = d

This is what I did and it was wrong... I'm not sure how to do this question. :/

The answer is t1 = 6.2 d = 1.2
• Feb 25th 2013, 08:37 AM
ibdutt
Re: Arthimetic Series 2
(2x-5)-(x) = 8.6 - (2x-5)
x-5 = 8.6 - 2x +5 = 13.6 - 2x
3x = 18.6 OR x = 6.2
I am sure you would have got it
• Feb 25th 2013, 09:24 AM
MINOANMAN
Re: Arthimetic Series 2
Mathnood
Next time for such kind of exercises use the basic property of Arithmetic Progression wich simply states that if 3 numbers a,b,and c are consecutive terms of an A.P then the mid term b is the arithmetic mean of the two others i.e : b=1/2[a+c]
Minoas
• Feb 26th 2013, 03:55 AM
Mathnood768
Re: Arthimetic Series 2
Thank you! I understand now!