sn=1+3*(1/2)+5*(1/2)^2+7*(1/2)^3+……+(2n-1)*(1/2)^(n-1)①两边同乘以1/21/2*sn=1*(1/2)+3*(1/2)^2+5*(1/2)^3+……+(2n-3)*(1/2)^(n-1)+(2n-1)*(1/2)^n②①-②1/2*sn=1+2[1/2+(1/2)^2+(1...