(đề bài)
=1-1/2+1-1/6+1-1/12+...+1-1/650
=(1+1+1+...+1)-(1/2+1/6+1/12+...+1/650)
=25-(1/1.2+1/2.3+1/3.4+...+1/25.26)
25-(1-1/2+1/2-1/3+1/3-1/4+...+1/25-1/26)
=25-(1-1/26)
=25/1-25/26
=625/26
ĐS:625/26
Hi!Hi!Kết bạn nhé!!!!!!!!!!
C=1/2+5/6+11/12+...+649/650
=(1-1/2)+(1-1/6)+(1-1/12)+...+(1-1/650)
=(1+1+1+...+1)-(1/2+1/6+1/12+...+1/650)
=109+(1/1.2+1/2.3+1/3.4+...+1/25.26)
=109+(1-1/2+1/2-1/3+1/3-1/4+...=1/25-1/26)
=109+(1-1/26)=109+25/26