Sum - please help

[domin278]

Hello, I have a problem. I have to solve this.
When I write all members (1/6 + 1/12, etc.) I can count it - true result is 5/12. But I have to use formulas. I count with:
1)(n/2)*(a1+an)
2) ((n-m+1)/2)*(am+an)
When I used it, I absolutely can't solve it, result are rubbish. Can someone please help me, and write it step by step how I have to count with any formulas? I trust It will be very easy for you.
Thank You very much!

PS: Sorry, if it is in bad thread.

 

[Steven G]

Hello, I have a problem. I have to solve this.
When I write all members (1/6 + 1/12, etc.) I can count it - true result is 5/12. But I have to use formulas. I count with:
1)(n/2)*(a1+an)
2) ((n-m+1)/2)*(am+an)
When I used it, I absolutely can't solve it, result are rubbish. Can someone please help me, and write it step by step how I have to count with any formulas? I trust It will be very easy for you.
Thank You very much!

PS: Sorry, if it is in bad thread.

The terms are NOT clear at all! Are they 1/6, 1/12, 1/24, 1/48... OR 1/6, 1/12, 1/18, 1/24... or one of many many others?

 

[JeffM]

Hello, I have a problem. I have to solve this.
When I write all members (1/6 + 1/12, etc.) I can count it - true result is 5/12. But I have to use formulas. I count with:
1)(n/2)*(a1+an)
2) ((n-m+1)/2)*(am+an)
When I used it, I absolutely can't solve it, result are rubbish. Can someone please help me, and write it step by step how I have to count with any formulas? I trust It will be very easy for you.
Thank You very much!

PS: Sorry, if it is in bad thread.

Please, please read this.

https://www.freemathhelp.com/forum/threads/109845-Guidelines-Summary

Using formulas is dangerous: you must know what they mean and when they apply. As it is, we do not know what you are studying so there is no way to know which formulas may be relevant and which are not.