求和2x1/2+4x1/4+6x1/8+8x1/16+…+2nx1/2^n要详解答案,急用!
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求和2x1/2+4x1/4+6x1/8+8x1/16+…+2nx1/2^n要详解答案,急用!
求和2x1/2+4x1/4+6x1/8+8x1/16+…+2nx1/2^n要详解答案,急用!
求和2x1/2+4x1/4+6x1/8+8x1/16+…+2nx1/2^n要详解答案,急用!
Sn=2x1/2+4x1/4+6x1/8+8x1/16+…+2nx1/2^n
1/2Sn=2x1/4+4x1/8+6x1/16+8x1/32+.2nx1/2^(n+1)
Sn-1/2Sn=2(1/2+1/4+1/8+1/16+1/32+.1/2^n)-n/2^n
Sn=4-1/2^(n-2)-n/2^n