观察下列算式,并进行计算:1/3×5=1/2×(1/3-1/5),1/5×7=1/2×(1/5-1/7)...求1/19×21+1/21×23+1/23×25+...1/97×99的值是多少
问题描述:
观察下列算式,并进行计算:1/3×5=1/2×(1/3-1/5),1/5×7=1/2×(1/5-1/7)...
求1/19×21+1/21×23+1/23×25+...1/97×99的值是多少
答
1/19×21+1/21×23+1/23×25+...1/97×99
=1/2*(1/19-1/21+1/21-1/23+1/23-1/25+……+1/97+1/99)
=1/2*(1/19-1/99)
=40/1881
答
1/19×21+1/21×23+1/23×25+...1/97×99
=1/2×(1/19-1/21+1/21-1/23+1/23-1/25+...+1/97-1/99)
=1/2×(1/19-1/99)
=40/1881
答
(*乘以号,/除以号)由已知有1/n*m=1/2*(1/n-1/m) 原式=1/2*(1/19-1/23)+1/2*(1/23-1/25)+…+1/2*(1/97-1/99) 提1/2出来,即:1/2*(1/19-1/23+1/23-1/25+1/97-1/99)=1/2*(1/19-1/99)=40/1881...