变形每一项比如
1/1*2*3=1/2(1/1*2-1/2*3)
1/2*3*4=1/2(1/2*3-1/3*4)
1/3*4*5=1/2(1/3*4-1/4*5)
.
.
.
1/98*99*100=1/2(1/98*99-1/99*100)
然后这些式子相加得
1/1*2*3+1/2*3*4+1/3*4*5+.1/98*99*100
=1/2(1/1*2-1/99*100)=4949/19800
变形每一项比如
1/1*2*3=1/2(1/1*2-1/2*3)
1/2*3*4=1/2(1/2*3-1/3*4)
1/3*4*5=1/2(1/3*4-1/4*5)
.
.
.
1/98*99*100=1/2(1/98*99-1/99*100)
然后这些式子相加得
1/1*2*3+1/2*3*4+1/3*4*5+.1/98*99*100
=1/2(1/1*2-1/99*100)=4949/19800