How to write summation expression in text file

For example, a [1] + a [2] + a [3] +... + a [n]
It can be expressed as sigma (I = 1, N, a [i])

RELATED INFORMATIONS

1. The square of x minus five x plus two equals 0? Find two values of X The square of 14x minus 13 equals 3? Finding two values of X
2. Each of the different letters in the following problem represents a different dight.If A=4,find the number M=_____ ,E=_____ ,T+______ . PU RPLE COMET + MEET ___________ AAAAAA
3. The square of X is 9. How much is x?
4. We can't separate the possible events from the possible events, Haizhou Haina company must pack five first-class products into a box when exporting a kind of parts. A worker mistakenly put two first-class products into a box when operating. Now he must inspect the second-class products and reload them into the first-class products. 1 if two first-class products are sampled each time, write down all the basic events 2 take two pieces at a time and find the probability of at least one second-class product (1) Two first-class products, one first-class product, one second-class product, two second-class products (2) C (2,1) C (3,1) + C (2,2)} / C (5,2) = 7 / 10, which means that it is possible to take one and another from two equal, and then add the possibility of taking all two equal, and divide by the total number of two equal. That's the probability of this problem, right? But why is it an equal possible event But the probability is 2 / 3, isn't it? Pick out two pieces that are either second-class or first-class Why not wait for a possible event
5. The square of x plus 10x plus 16 equals 0
6. The algorithm of the answer to a probability question is C14 (4 below) * C16 (6 below) / c210 (10 below) = 5 / 18?
7. Whose domain of definition is required in y = LG (x2 + ax + 2), X or the whole formula of x2 + ax + 2
8. The square of x minus 10x plus 25 equals 0. How much does x equal?
9. The function f (x) = ax ^ 2 + 2 (A-3) + 1 is a decreasing function in the interval (- 2, + ∞). Find the value range of real number a!
10. How to calculate the results of five five, using + - * / four operation symbols each time, which are equal to 2,3,4,6 respectively
11. Given that x minus 1 / x equals 2, how much is x square minus 1 / x square? Specific and accurate answers and processes are needed
12. What is the formula for horizontal summation?
13. 2X + 3Y = k the sum of solutions X and y of the system of linear equations {3x-4y = K + 11} with respect to X and Y is known to be equal to 3, and the value of K is obtained The method is as simple as possible
14. Summation formula of permutation and combination
15. If the solutions of the equations 2x-y23 and x-2y equal to a satisfy that x + y is greater than 0, then the value range of a is a, and the value range of a is a
16. Given the complex number Z, find Z + Z square + Z three square + Can we use the summation formula of real number equal ratio sequence to sum?
17. To solve the equation about X, the square of x minus 2x plus 1 equals K (the square of x minus 1) (k is not equal to 0)
18. Is there a formula for summation of second order arithmetic sequence? Is the latter minus the former is the arithmetic sequence, how to find the sum of the original sequence?
19. If a is not equal to 0, then the equation of X + the square of Y + ax ay = the image represented by 0 On X-axis symmetry On Y-axis symmetry On the symmetry of the line X-Y = 0 On the symmetry of the line x + y = 0
20. Who knows the summation formula of second order arithmetic sequence?