1*3/1+2*4/1+3*5/1+4*6/1.+18*20/1怎么算?
问题描述:
1*3/1+2*4/1+3*5/1+4*6/1.+18*20/1怎么算?
答
1/1×3+1/3×5+1/5×7+……+1/17×19+1/2×4+1/4×6+1/6×8+……+1/18×20=1/2×﹙1-1/3+1/3+1/5+……+11/17-1/19﹚+1/2×﹙1/2-1/4+1/4-1/6+……+1/18-1/20﹚=1/2×﹙1-1/19﹚+1/2×﹙1/...