1+2+2的平方+2的立方+2的(立方+1)·····+2的(立方+9)要过程1+2+2的平方+2的立方+2的(立方+1)················2的(立方+6)前面错了
来源:学生作业帮助网 编辑:作业帮 时间:2024/11/06 00:19:22
1+2+2的平方+2的立方+2的(立方+1)·····+2的(立方+9)要过程1+2+2的平方+2的立方+2的(立方+1)················2的(立方+6)前面错了
1+2+2的平方+2的立方+2的(立方+1)·····+2的(立方+9)
要过程
1+2+2的平方+2的立方+2的(立方+1)················2的(立方+6)前面错了
1+2+2的平方+2的立方+2的(立方+1)·····+2的(立方+9)要过程1+2+2的平方+2的立方+2的(立方+1)················2的(立方+6)前面错了
这是个等比数列求和问题.S=(1-2^10)/(1-2)=2^10-1=1023
直接用等比公式计算就可以了
n = 1, S = 2^0 = 1
n = 2, S = 2^0 + 2^1 = 1 + 2 = 3
n = 3, S = 2^0 + 2^1 + 2^2 = 1 + 2 + 4 = 7
n = 4, S = 2^0 + 2^1 + 2^2 + 2^3 = 1 + 2 + 4 + 8 = 15
n = n, S = 2^0 + 2^1 + 2^2 + 2^3 + ...
全部展开
n = 1, S = 2^0 = 1
n = 2, S = 2^0 + 2^1 = 1 + 2 = 3
n = 3, S = 2^0 + 2^1 + 2^2 = 1 + 2 + 4 = 7
n = 4, S = 2^0 + 2^1 + 2^2 + 2^3 = 1 + 2 + 4 + 8 = 15
n = n, S = 2^0 + 2^1 + 2^2 + 2^3 + ....+ 2^(n-2) + 2^(n-1)
2S = 2 * (2^0 + 2^1 + 2^2 + 2^3 + .... + 2^(n-1)) = 2^1 + 2^2 + 2^3 + ....+ 2^(n-1) + 2^n
=>
S = 2S - S = 2^1 + 2^2 + 2^3 + .... + 2^n - (2^0 + 2^1 + 2^2 + 2^3 + .... + 2^(n-1)) = 2^n - 1
S = 2^0 + 2^1 + 2^2 + 2^3 + .... + 2^(n-1) = 2^n - 1
1+ 2^2 + 2^3 + ..... + 2^9 => n-1 = 9
n = 10 =>S = 2^10 - 1 = 1023
收起