=2/4+2/28+2/70+...+2/9118+2/9700=2.(1/4+1/28+1/70+...+1/9118+1/9700)
=2.(1/1.4+1/4.7+1/7.10+...+1/94.97+1/97.100)
=23.(1/1−1/4+1/4−1/7+1/7−1/10+...+1/94−1/97+1/97−1/100)
=23.[1/1+(−1/4+1/4)+(−1/7−1/7)+(−1/10+1/10)+...+(−1/94+1/94)+(−1/97+1/97)−1/100
=23.(1/1−1/100)
=23.99100
=33/50
Hơi khó nhìn, khi nào rảnh thì sửa cho em nhé !