解方程(2n+1)(n+1)n-(2n-21)(n-10)(n-11)=2(2n-9)(n-4)(n-5)
2^n/n*(n+1)
证明不等式:(1/n)^n+(2/n)^n+(3/n)^n+.+(n/n)^n
Sn=n(n+2)(n+4)的分项等于1/6[n(n+2)(n+4)(n+5)-(n-1)n(n+2)(n+4)]吗?
证明(1+2/n)^n>5-2/n(n属于N+,n>=3)
lim 9^n+4^n+2/5^n-3^2n-1 n趋于无穷大时
阶乘(2n-1)!=(2n)!/(2^n*n!
[3n(n+1)+n(n+1)(2n+1)]/6+n(n+2)化简
1 + (n + 1) + n*(n + 1) + n*n + (n + 1) + 1 = 2n^2 + 3n + 3
证明:1+2C(n,1)+4C(n,2)+...+2^nC(n,n)=3^n .(n∈N+)
化简:1/(n+1)(n+2)+1/(n+2)(n+3)+1/(n+3)(n+4)
(n+1)(n+2)/1 +(n+2)(n+3)/1 +(n+3)(n+4)/1
化简(n+1)(n+2)(n+3)