-1 + 3-5 + 7-9 + 11 -... + 2011-2013 + 2015

-1 + 3-5 + 7-9 + 11 -... + 2011-2013 + 2015

The original formula = (- 1 + 3) + (- 5 + 7) + (- 9 + 11) -... + 2011 + (- 2013 + 2015)
=2+2+2+…… +2, a total of (2015 + 1) △ 4 = 504 groups
=2*504
=1008

Let {an} satisfy A1 = 0,1 / (1-an + 1) - 1 / (1-an) = 1
Let {an} satisfy A1 = 0,1 / (1-an + 1) - 1 / (1-an) = 1 (1) to find the general term formula of {an} (2) let BN = (1 - (an + 1) 1 / 2) / (n) 1 / 2, denote Sn = B1 + B2 + +BN, proving Sn & lt; 1

1/（1-a(n+1)）-1/（1-an）=1
1 / (1-an) is an arithmetic sequence
First item 1 / (1-a1) = 1
∴1/(1-an)=1+(n-1)*1=n
∴1-an=1/n
an=1-1/n
The second question is shown in the picture

Sequence an + 2snsn-1 = 0 (n ≥ 2), A1 = 1 / 2
It is known that the sum of the first n terms of the sequence {an} is Sn (SN ≠ 0), and satisfies an + 2snsn-1 = 0 (n ≥ 2), A1 = 1 / 2 [one of sn-1 is s (n-1)!]
(1) Prove: {1 / Sn} is arithmetic sequence
(2) The formula of {an} general term

（1）
（2）

What is the square of minus five?

-5*-5=25 .

The times of the negative quadratic of five
Is the negative quadratic of five quadratic or negative quadratic

Negative quadratic power
The negative square of five is 1 / 25

Summation of sequence
Find out the general term formula of the following sequence:
1、
a1=1
an=
n
∑=（n/u）
u=1
(i.e. (n / 1) + (n / 2) + (n / 3) +... (n / N))
1、
a1=1
an=
n
∑=（u/n）
u=1
(i.e. (1 / N) + (2 / N) + (3 / N) +... (n / N))
Note that the simplified general term formula of the ball is not the sum of the general term formula of the ball.

1.Sn=
=When I think about it, I have the impression that (n / 1) + (n / 2) + (n / 3) +... (n / N) has a formula, but I can't remember it
2.an=（1/n）+（2/n）+（3/n）+...（n/n）=(1+n)/2
sn=(1+(1+n)/2)*n/2=(3+n)*n/4

The reciprocal of the sum of five consecutive odd numbers is 145. What is the largest odd number among the five odd numbers?

If the sum of the five consecutive odd numbers is 45, 45 △ 5 = 9, then the largest one is 9 + 2 + 2 = 13. A: the largest one among the five odd numbers is 13

The reciprocal of the sum of five consecutive odd numbers is one fortieth. What is the largest odd number among the five odd numbers?

The title is indeed wrong
It is well known that the sum is even when the sum of odd numbers is even
5 is odd, so sum must be odd
The reciprocal of one in forty is 40
So there is no solution to this problem
The reciprocal of five consecutive even sums is one in forty

The difference between the reciprocal of two consecutive odd numbers is 2 / 323. What is the sum of these two consecutive odd numbers?

323=17x19
So these two odd numbers are 17 and 19
So the sum of these two consecutive odd numbers is 17 + 19 = 36

The sum of any two odd numbers must be even______ (judge right or wrong)

According to the properties of odd and even numbers, the sum of any two odd numbers must be even