=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)=2.(1/1−1/4+1/4−1/7+1/7−1/10+...+1/94−1/97+1/97−1/100)=2.[1/1+(−1/4+1/4)+(−1/7−1/7)+(−1/10+1/10)+...+(−1/94+1/94)+(−1/97+1/97)−1/100$=2.(1/1-1/100)$$=2.(100/100-1/100)$$=2.99/100$$=99/50=1\tfrac{49}{50}$Hơi khó nhìn, khi nào rảnh thì sửa cho em nhé !
=2/4+2/28+2/70+...+2/9118+2/9700=2.(1/4+1/28+1/70+...+1/9118+1/9700)=2.(1/1.4+1/4.7+1/7.10+...+1/94.97+1/97.100)$=
\frac{2
}{3}.(1/1-1/4+1/4-1/7+1/7-1/10+...+1/94-1/97+1/97-1/100)$$=
\frac{2
}{3}.[1/1+(-1/4+1/4)+(-1/7-1/7)+(-1/10+1/10)+...+(-1/94+1/94)+(-1/97+1/97)-1/100$$=
\frac{2
}{3}.(1/1-1/100)$$=
\frac{2
}{3}.
\frac{99
}{100
}$$=
33/50$Hơi khó nhìn, khi nào rảnh thì sửa cho em nhé !