What does 1 + 3 + 5 + 7 + 9. + (2n-1) equal According to 1 + 3 = half (1 + 3) × 2, 1 + 3 + 5 = half (1 + 5) × 3

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• 1. 1 + 3 = (1 + 3) * 2 / 2; 1 + 3 + 5 = (1 + 5) * 3; 1 + 3 + 5 + 7 = (1 + 7) * 4 / 2 ', (2n-1) is equal to? a n*n b (n+1)*(n+1) c (1+n)*n/2 d (n+1)*n/2
• 2. lim n→∞ [(n+1)^4/5^(n+1)]/[n^4/5^n] Why is it equal to 1 / 5,
• 3. Calculate LIM (a - 2 + a - 4 +...) +a⌒2n)/（a+a⌒2+a⌒3＋… +a⌒n）
• 4. How to find the sum function of (n = 1, ∞) Σ n * x ^ (n-1) power series? I think the answer is 1 / (1-x). Why is 2n missing?
• 5. Sum function of power series ∑ (n = 1 to ∞) [(- 1) ^ (n-1) / (n + 1)] (x-1) ^ n What if n = 0
• 6. Can 1-cost be replaced by 1-cost ~ x ^ 2 / 2 when Lim t tends to 0 T / radical? Why is there no limit
• 7. Finding the limit of (ln1 / x) ^ x when x approaches 0 from the right
• 8. a1=2,a(n+1)=1/2(an+2/an),n=1,2,3…… Prove LIM (an) = root 2, n tends to infinity
• 9. Given the first N-term of sequence an and Sn = 2n, find its general term formula
• 10. Determinant calculation: 123... N234... 1345... 2. N12... N-1 rt The first line is 1 to N, the second line is 2 to N, and then add a 1. The third line is n items starting from 3, and so on. The first item in the last line is n, and then 1 to n-1. Each line is composed of 1 to n
• 11. Fill in the eight vertices of a square with the eight numbers of - 1, - 2, - 3, - 4, - 5, - 6, - 7, - 8. Each vertex can only fill in one number, so that the sum of the four vertices on the six faces of the square is equal
• 12. 2/1*4/3*6/5*8/7*.（2n）/（2n-1）＞√（2n+1）
• 13. ① The power of  (x) =  / 178 + 1
• 14. When n is odd, the nth power of 2 * 7 and the nth power of 3 is the nth power of =? (- 42) The nth power of 2 * the nth power of 7 * the nth power of 3 divided by the nth power of (- 42)
• 15. Let the probability density of the population X be f (x, θ), where θ has unknown parameters, and E (x) = 2 θ, x1, X2 Xn is a sample from population X - x is the sample mean value, CX & # 175; is the unbiased estimate of θ (Cx - is the mean value of C multiplied by x), then what is the constant C equal to
• 16. Let the probability density of population X be f (x; θ) = e ^ - (x - θ), when x > = 0; f (x; θ) = 0, X
• 17. How to find LIM (x → 0 +) [(x ^ x-1) / xlnx]?
• 18. What is the limit of xlnx + X when x tends to zero
• 19. If the quotient of natural number a divided by natural number B is 9, then the greatest common factor of a and B is () reason
• 20. m. N is a non-zero natural number, m × 25 of N & lt; m, m × 22 of N & gt; m, find the value of n!