Tn=5/2^1+7/2^2+9/2^3+…+(2n+3)/2^n ①
∴ Tn/2=5/2^2+7/2^3+…+(2n+1)/2^n+(2n+3)/2^(n+1) ②
①-②,得：Tn/2=5/2+2/2^2+2/2^3+…+2/2^n-(2n+3)/2^(n+1)
=5/2+1/2^1+1/2^2+…+1/2^(n-1)-(2n+3)/2^(n+1)
=5/2+1/2*[1-(1/2)^(n-1)]/(1-1/2)-(2n+3)/2^(n+1)
=7/2-(1/2)^(n-1)-(2n+3)/2^(n+1)
=7/2-(1/2)^(n+1)*[4+(2n+3)]
=7/2-(1/2)^(n+1)*(2n+7)
∴Tn=7-(1/2)^n*(2n+7)
令f(x)=7-(1/2)^x*(2x+7)=7-(2x+7)/2^x (x≥1)
則：f'(x)=-[2*2^x-(2x+7)*2^x*ln2]/(2^x)^2
=-[2-(2x+7)*ln2]/(2^x)
∵2-(2x+7)*ln2=2-7ln2-2xln2