Question 1184341: 1.Find the arithmetic mean between -2,___18
2.Find the sum of sequence -30,-15,0,15,30,...
It's fine if you don't show the solution just the answer, thanku^^
Answer by ikleyn(52790)   (Show Source):
You can put this solution on YOUR website! .
1. The arithmetic mean of the numbers -2 and 18 is half of their sum  =  = 8.
2. Regarding your sequence, I see 5 terms there -30, -15, 0, 15, 30.
Then I see ellipsis, that says me nothing.
The sum of the five written terms is equal to zero.
If you mean something different, then take a labor to describe this "something" adequately.
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For arithmetic sequences, there are well known formulas, written everywhere, in any textbook or in numerous Internet sites.
For example, you may look into the lessons
- Arithmetic progressions
- The proofs of the formulas for arithmetic progressions
- Problems on arithmetic progressions
- Word problems on arithmetic progressions
in this site and to learn the subject from there . . .
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