Summation Operator

[Sapphy]

Hi,
I'm trying to work out a way of getting Excel 2003 to answer

y=2i+1 when i=1 initially with a final value of 10.
y=(2x1+1)+(2x2+1)+...+(2x10+1)

I could type it by hand however my next question requires the upper limit n
to be infinity for the eqn

y=1/i(i-1) when i=1 initially and the final value for i=infinity
y=(1/(1(1+1))+(1/2(2+1)+...(1/infinity(infinity+1)

and I eed to find the approximate answer for y when the addition of the
successive terms causes a lass than 0.0001% change in y, as well as the last
value for i when the program stops.

Am utterly stumped! Please help,

Thank you.

 

[Gary''s Student]

In A1 enter:
..5
In A2 enter:
=A1+1/(ROW()*(ROW()+1)) and copy down
In B2 enter:
=(A2-A1)/A1 and copy down

For the first 10 rows:

0.50000000
0.66666667 33.3333333333%
0.75000000 12.5000000000%
0.80000000 6.6666666667%
0.83333333 4.1666666667%
0.85714286 2.8571428571%
0.87500000 2.0833333333%
0.88888889 1.5873015873%
0.90000000 1.2500000000%
0.90909091 1.0101010101%

and for rows 999 thru 1002:

0.99900000 0.0001002004%
0.99900100 0.0001000001%
0.99900200 0.0000998004%
0.99900299 0.0000996013%

so for i>1000 the relative change term-to-term will be under your limit.