# Can someone tell me why my geometric progress is not coming out right? image incuded

1. Nov 10, 2006

### mr_coffee

Hello everyone i'm studying for my next exam and I screwed up on the geometric progressions and arthm and they are the easiest of them all but I dont know what i'm doing wrong.

The first problem on the exam said:
Suppose that an arithmetic series has 202 terms. If the first term is 4PI and the last term is 60-4PI, what is the sum of the sries?

I came out with 6060, my work is posted below ( i think i got it right this time)

Now for the real problem, Write down the formula of the following sum:
You can see my work at the bottom but as you can see, it doesn't check out with adding up the terms by hand and usuing my formula. I'm really not sure what I did wrong here. ANy help would be great:
http://suprfile.com/src/1/4apu96r/lastscan.jpg [Broken]

Also another one is #3. It says Write down the formula of the sum, simplify your answer, and now check when n = 1, n = 2, n = 3.

Again the formula and adding the terms up by hand arn't working out.
http://suprfile.com/src/1/4apvbsk/lastscan.jpg [Broken]

Last edited by a moderator: May 2, 2017
2. Nov 10, 2006

### Office_Shredder

Staff Emeritus

You got the first question right though

3. Nov 10, 2006

### mr_coffee

Thanks for the responce, how about now?
http://suprfile.com/src/1/4apu96r/lastscan.jpg [Broken]

and

http://suprfile.com/src/1/4apvbsk/lastscan.jpg [Broken]

Last edited by a moderator: May 2, 2017
4. Nov 11, 2006

### drpizza

Just a quick glance... one error that seemed to pop out at me is,

Check (3/2)^2. I think it was just a careless mistake; you didn't put parentheses around the 3/2 and ended up forgetting to square the denominator as well.