1+3+5+7+9+11+.+(2n-1)=( )2次方求求你们了,1分钟

解方程(2n+1)(n+1)n-(2n-21)(n-10)(n-11)=2(2n-9)(n-4)(n-5) lim(3^2n+5^n)/(1+9^n)3^2n or 5^n lim(3^2n+5^n)/(1+9^n)=? 数学归纳法难题1/2+1+3/2+...+n/2=n(n+1)/4和1*5+2*7+...+n(2n+3)=n(n+ 1)(4n+11)/6,利用上述式子证明对于所有正整数n,1*4+2*6+...+n(2n+2)=2n(n+1)(n+2 )/3 3(n-1)(n+3)-2(n-5)(n-2) 2^n*3^n*5^(n+1)/30^n 证明不等式：(1/n)^n+(2/n)^n+(3/n)^n+.+(n/n)^n 1.（双选）一个10N的力可以分解为下面哪两个力?A.30N 5N B.20N 5N C.10N 5N D.10N 10N2..（双选）物体受共点力F1 F2 F3 作用匀速直线运动.这三个力的数值选取可能正确的是A.15N 5N 6N B.9N 2N 7N C.3N 4N 5N D.1N n+(n+1)+(n+2)+(n+3)+(n+4)=5n+10这道题怎么解 ansys直接建立有限元模型问题finish/clear/prep7n,1,0,0,0n,2,0,0.5,0n,3,0,1,0n,4,0.5,1,0n,5,1,1,0n,6,1,0.5,0n,7,1,0,0n,8,0.5,0,0n,9,0,0,0.5n,10,0,1,0.5n,11,1,1,0.5n,12,1,0,0.5n,13,0,0,1n,14,0,0.5,1n,15,0,1,1n,16,0.5,1,1n,17,1,1,1n,18,1,0.5,1n 1/[n(n+1)]+1/[(n+1)(n+2)]+1/[(n+2)(n+3)]+1/[(n+3)(n+4)]+[(n+4)(n+5)}怎么算谢谢了, 1+2+3+4+5+6+7+8+9+…+n=n(n+1)/2 1+3+5+7+9+11+13+15+…+(2n-1)=n2 2+4+6+8+10+12+14+…+(2n)=n(n+1) 12+1+2+3+4+5+6+7+8+9+…+n=n(n+1)/2 1+3+5+7+9+11+13+15+…+(2n-1)=n2 2+4+6+8+10+12+14+…+(2n)=n(n+1) 12+22+32+42+52+62+72+82+…+n2=n(n+1)(2n+1)/6 13+ 1+3+5+7+9+.+(2n-1)+(2n+1)+(2n+3)= 若3^n+1*5^n+1=15^2n-7,则n=多少 1+3+5+7+9+11+.+（2n-3)＋（2n-1）+（2n+1） 计算 n为正整数,3+5+7+9+.(2n+1)=168,则n= 1/3a^2n -(-7a^n)+(-1)^2n+1 a^n -(2/5a^2n)-5a^n(n为正整数） (急!）下列哪一组力作用在同一物体上,可以构成合力与分力的关系A.5N,3N,4N,8N,B.10N,8N,2N,1N,C.10N,20N,30N,40N,D.3N,7N,2N,1N,