-2;ak-2 (k-2项) k-1+2-1+2-+…2k-1+9k-1 2(1-2),2(1-2 2-(1-22) (2-21)+(2k-22)+…+(2k-2*-2)+(2k-2k-1) (k-1)2-[2+22+…2-] 2(1-2) 所以∑(k-)21=(2-1)k-24(k=2)-2=24#-k-2 另1:令s=∑j21=1*20+22+3*2+…,+h >2s=1*2+2*2-+3*2+…+h米 2(1-2b) 亦即∑j=(h-2)2-1+1 两边乘2得:∑p2=h-2)2+2 另2:令s(x)=2 2 +2 2 + 2 3 +2 3 +2 3 +… 2 k -2 +2 k -2 +2 k -2 +…+2 k -2 +… (k-2 项) 2 k -1 +2 k -1 +2 k -1 +…2 k -1 +2 k -1 (k-1 项) = 1 2 2 (1 2 ) 1 2 2 (1 2 ) ... 1 2 2 (1 2 ) 1 2 2 (1 2 ) 1 1 2 2 2 2 1 1 - - + - - + + - - + - - k- k- k - k - =(2 k -21 )+(2 k -2 2 )+…+(2 k -2 k -2 )+(2 k -2 k -1 ) =(k-1) 2 k -[21 +2 2 +…2 k -1 ] =(k-1) 2 k - 1 2 2 (1 2 ) 1 1 - - k- =(k-1) 2 k +2-2 k =2 k (k-2)+2 所以 j k j (k j)2 1 0 å - = - =(2 k -1)k-2 k (k-2)-2=2 k +1 -k-2 另 1：令 s=å= - h j 1 j 1 j2 =1*2 0 +2*21 +3*2 2 +…+h*2 h-1 =>2s=1*21 +2*2 2 +3*2 3 +…+h*2 h =>s-2s=2 0 +21 +2 2 +…+2 h-1 -h*2 h = 1 2 2 (1 2 ) 0 - - h - h*2 h =>s= h*2 h - 2 h +1 亦即å - = - h 1 j 1 j 1 j2 =(h-2) 2 h-1 +1 两边乘 2 得: å - = h 1 j 1 j j2 =(h-2) 2h +2 另 2：令 s(x)= å= - h j 1 j 1 jx 则