求怎么化简成这样的Tn=b1+b2+...+bn=1×2^1+3×2^2+5×2^3+...+(2n-1)×2^n2Tn=1×2^2+3×2^3+...+(2n-3)×2^n+(2n-1)×2^(n+1)Tn-2Tn=-Tn=2^1+2×2^2+2×2^3+...+2×2^n-(2n-1)×2^(n+1)此处上一步到下一步怎么化简的?=2+2×4×[2^(n-1) -1]/(2-1) -(2n-1)×2^(n+1)=(3-2n)×2^(n+1)-6Tn=(2n-3)×2^(n+1) +6.求指导

求怎么化简成这样的
Tn=b1+b2+...+bn=1×2^1+3×2^2+5×2^3+...+(2n-1)×2^n
2Tn=1×2^2+3×2^3+...+(2n-3)×2^n+(2n-1)×2^(n+1)
Tn-2Tn=-Tn=2^1+2×2^2+2×2^3+...+2×2^n-(2n-1)×2^(n+1)
此处上一步到下一步怎么化简的?
=2+2×4×[2^(n-1) -1]/(2-1) -(2n-1)×2^(n+1)
=(3-2n)×2^(n+1)-6
Tn=(2n-3)×2^(n+1) +6.
求指导