求和sn=1*2¹+3*2²+5*2³+...+(2n-1)*2ˆn
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求和sn=1*2¹+3*2²+5*2³+...+(2n-1)*2ˆn
sn=1*2¹+3*2²+5*2³+...+(2n-1)*2ˆn.(1)
2Sn=1*2^2+3*2^3+5*2^4+.+(2n-3)*2^(n)+(2n-1)*2^(n+1).(2)
(1)-(2)
Sn=2+2[2^2+2^3+...+2^(n)]-(2n-1)*2^(n+1)
=-2+2[2+2^2+2^3+...+2^(n)]-(2n-1)*2^(n+1)
=-2+2[2(1-2^(n))/(1-2)]-(2n-1)*2^(n+1)
=2^(n+2)-(2n-1)*2^(n+1)-4
=2^(n+1)[-2n-1/2]-4
2Sn=1*2^2+3*2^3+5*2^4+.+(2n-3)*2^(n)+(2n-1)*2^(n+1).(2)
(1)-(2)
Sn=2+2[2^2+2^3+...+2^(n)]-(2n-1)*2^(n+1)
=-2+2[2+2^2+2^3+...+2^(n)]-(2n-1)*2^(n+1)
=-2+2[2(1-2^(n))/(1-2)]-(2n-1)*2^(n+1)
=2^(n+2)-(2n-1)*2^(n+1)-4
=2^(n+1)[-2n-1/2]-4
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