1/2+/2/2*3+3/2*3*4=0.5+2/2*3+3/2*3*4=0.5+1*3+3/2*3*4=0.5+3+1.5*3*4=0.5+3+18=21.5
裂项原式=1/2+1/3+1/8 =23/24
1/2+2/2*3+3/2*4=3/2*3+3/2*4=3/2*(3+4)=3/2*7=21/2
45
题有点问题