1*3/1+3*5/1+5*7/1+.+99*101/1
=1/2*(1-1/3)+1/2*(1/3-1/5)+1/2*(1/5-1/7)+……+1/2*(1/99-1/101)
=1/2*(1-1/3+1/3-1/5+1/5-1/7+……+1/99-1/101)
=1/2*(1-1/101)
=1/2*(100/101)
=50/101
1/3表示三分之一,其他都一样
1*3/1+3*5/1+5*7/1+.+99*101/1
=1/2*(1-1/3)+1/2*(1/3-1/5)+1/2*(1/5-1/7)+……+1/2*(1/99-1/101)
=1/2*(1-1/3+1/3-1/5+1/5-1/7+……+1/99-1/101)
=1/2*(1-1/101)
=1/2*(100/101)
=50/101
1/3表示三分之一,其他都一样