SOLUTION: in an arithmetic sequence, a1=2 and a40=80. what is the value of the sum of all even terms only?

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Question 411233: in an arithmetic sequence, a1=2 and a40=80. what is the value of the sum of all even terms only?
Answer by MathLover1(6813) About Me  (Show Source):
You can put this solution on YOUR website!

To find the sum of a certain number of terms of an arithmetic sequence:
Sn=n%28a1%2Ban%29%2F2
where Sn is the sum of n terms (nth partial sum), a1 is the first term, an is the nth term

given: a1=2 and a40=80
to find: the sum of a2+a4+a6+a8+...a40
Sn=n%28a1%2Ban%29%2F2

S%2811%29=11%282%2B24%29%2F2


S%2811%29=11%2A24%2F2

S%2811%29=11%2A12


S%2811%29=132