拆项法.)
拆项法.)
拆项法.)
拆项法.)
(8)原式=2(1/11-1/12+1/12-1/13+.+1/54-1/55)
=2(1/11-1/55)
=2*4/55
=8/55
(9)原式=1/2(1/2-1/4+1/4-1/6+.+1/48-1/50)
=1/2(1/2-1/50)
= 6/25
图片太黑看不清我重发
拆项法.)
拆项法.)
拆项法.)
(8)原式=2(1/11-1/12+1/12-1/13+.+1/54-1/55)
=2(1/11-1/55)
=2*4/55
=8/55
(9)原式=1/2(1/2-1/4+1/4-1/6+.+1/48-1/50)
=1/2(1/2-1/50)
= 6/25
图片太黑看不清我重发