- 初中数学题目1/1*3+1/2*4+1/3*5+.....+1/
- 1/1*3+1/2*4+1/3*5+.....+1/18*20=?
- 1/1*3+1/2*4+1/3*5+.....+1/18*20
=1/2*(2/1*3+2/2*4+2/3*5+.....+2/18*20)
=1/2[(3-1)/1*3+(4-2)/2*4+(5-3)/3*5...+(20-18)/18*20]
=1/2*(1-1/3+1/2-1/4+1/3-1/5+...+1/18-1/20)
=1/2(1+1/2-1/19-1/20)
=(1/2)*(531/380)
=531/760