数学北大绿卡人教版六年级上册第20页的数学小博士怎么写?1/1987*1988+1/1988*1989+1/1989*1990+1/1990=1/1987*1988+1/1988*1989+1/1989*1990+1989/1989*1990(后两个相加)=1/1987*1988+1/1988*1989+（1+1989）/1989*1990=1/1987*1988+1/1988*1989+1/1989=1/1987*1988+1/1988*1989+1988/1988*1989(后两个相加)=1/1987
2019-05-22
数学北大绿卡人教版六年级上册第20页的数学小博士怎么写?
1/1987*1988+1/1988*1989+1/1989*1990+1/1990
=1/1987*1988+1/1988*1989+1/1989*1990+1989/1989*1990
(后两个相加)
=1/1987*1988+1/1988*1989+（1+1989）/1989*1990
=1/1987*1988+1/1988*1989+1/1989
=1/1987*1988+1/1988*1989+1988/1988*1989
(后两个相加)
=1/1987*1988+（1+1988）/1988*1989
=1/1987*1988+1/1988
=1/1987*1988+1987/1987*1988
=(1+1987)/1987*1988
=1/1987 复制下来!
优质解答
从后面往前面加,通分很容易的得知结果1987分之1
从后面往前面加,通分很容易的得知结果1987分之1