What is the formula of 1 + 3 + 5 + 7 +... + 99 = () arithmetic sequence

What is the formula of 1 + 3 + 5 + 7 +... + 99 = () arithmetic sequence

Sn=[n(a1＋an)]/2=na1＋[n(n－1)]d/2
The result is 50 & sup2; = 2500
General formula of arithmetic sequence:
an=a1+(n-1)d
Where A1 is the first term and D is the tolerance (such as d = a2-a1, etc.)
Sum formula:
Sn=[n(a1＋an)]/2=na1＋[n(n－1)]d/2
The answer to this question is: n = 50; d = 2, A1 = 1
Sn=1+3+5+7+...+99=50*49*2/2+50*1=2450 +50=2500
(first item + last item) x number of items / 2
[(1+99)x50]/2
2500; the above is for reference only! Question: there is no such option as 2500
Xiao Li read a 90 page story book, has read 70 pages, has read a few parts of the book
In a hurry
Come on, come on, come on
Today is the day
seventy-ninetieths
Simple operation of 10.25-6.15-3.85 + 7.75
10.25-6.15-3.85+7.75
=10.25+7.75-(6.15+3.85)
=18-10
=8
Solving one math problem in high school
In the sequence {a n}, A1 = 1 / 2, the first n terms and Sn = n ^ 2 · an, find the general term formula a n
a1=1/2 ,Sn=n^2*an
Then s (n-1) = (n-1) ^ 2 * a (n-1)
By subtracting the two formulas, an = n ^ 2 * an - (n-1) ^ 2 * a (n-1)
We obtain an / a (n-1) = (n-1) / (n + 1)
Similarly, a (n-1) / a (n-2) = (n-2) / n
a(n-2)/a(n-3)=(n-3)/(n-1)
……
a3/a2=2/4
a2/a1=1/3
a1=1/2
The product of the left is equal to the right
We get an = 1 / (n ^ 2 + n) = 1 / [n (n + 1)]
n=1,a1=1/2,S1=1/2
n=2,4a2=a2+1/2,a2=1/6,S2=2/3
n=3,9a3=a3+2/3,a3=1/12,S3=3/4
.....
an=1/[n(n+1)]
Sn-1=(n-1)^2*an-1
Subtracting an = n ^ 2 · an - (n-1) ^ 2 * an-1
So (n + 1) an = (n-1) an-1 an = (n-1) / (n + 1) an-1
So an = (n-1) / (n + 1) * (n-2) / N * (n-3) / (n-1)... * 1 / 3A1 = 1 / (n + 1)
Test A1 is also consistent
an=sn-s(n-1)=n^2an-(n-1)^2a(n-1)
(n^2-1)an=(n-1)^2a(n-1)
an=a(n-1)*((n-1)/(n+1))
an=((n-1)/(n+1))*a(n-1)=((n-1)/(n+1))*((n-2)/(n))*a(n-2)
=...=((n-1)/(n+1))*((n-2)/(n))*((n-3)/(n-1))*......*((2-1)/(2+1))a1
=2/(n(n+1))*a1=1/n(n+1)
an=1/(n(n+1))
Answer [+ 1] / (n)
Brief process an = SN-S (n-1) = n ^ 2 · an - (n-1) ^ 2 · a (n-1)
=>an=(n-1)/(n+1) *a(n-1)
Expanding recursive reduction an = 2 / (n + 1) * 1 / N * A1
Mingming read a story book, the first day read 1 / 5 of the whole book, the second day read 1 / 4 of the whole book, the second day read 8 pages more than the first day, how many pages are there in the story book
8/(1/4 -1/5)=160
222.85-333.46 + 332.15-111.54
It is helpful for the responder to give an accurate answer
（222.85+332.15）-（333.46+111.54）
=555-445
=110
Mathematical problems recursive sequence of general formula!
1=5，2=25，3=45，4=175，5=？
Is it a recursive sequence? If yes, please tell me the answer and the general formula.
It's not logic. It's Harvard. It's like the answer is
5=1
Read a story book, the first day read 1 / 5, the second day read the remaining 1 / 4, the third day read 12 pages, left half of the whole book, how many pages does this book have?
12 divided by 3 is equal to 4, 4 divided by one fifth is equal to 20 pages, this problem is very simple, just draw a line diagram to solve it
Ask a math problem
0.9+99x0.9
=
=
=89.91
0.9+99x0.9
=0.9x(1+99)
=0.9x100
=90
0.9+99x0.9
=0.9×（1+99）
=0.9×100
=90
Is the title wrong
0.9+99x0.9
=0.9*(99+1)
=0.9*100
=90
General term formula of 1 3 5 sequence
There are two straight lines with at most one intersection, three lines with three intersections, four lines with six intersections, ten lines with at most several intersections, it is required to use the method of sequence to solve this problem
This is adjacent two phases and increasing. This problem is meaningless. There are still many rules that have not been explained. 1 33 5 13 27 51... (1 + 3 third term) * 2 = (3 second term + 5) and * 2 = (3 third term + 13)
1 3 6 10 15.an=a(n-1) +(n-1)
an=n*(n-1)/2