Question

Tính tổng S=1/1.3 +1/2.4+ 1/3.5+....+1/7.9 +1/8.10

Answer 1

S=(1/1.3+1/3.5+.....+1/7.9) + (1/2.4+1/4.6+....+1/8.10)

2S=1/2.(1-1/9+(1/2-1/10))

2S=1/2.(8/9 + 2/5)

2S=1/2.58/45

2S=29/45

S=29/45:2

S=29/90

Answer 2

S=(1/1.3+1/3.5+.....+1/7.9) + (1/2.4+1/4.6+....+1/8.10)

2S=1/2.(1-1/9+(1/2-1/10))

2S=1/2.(8/9 + 2/5)

2S=1/2.58/45

2S=29/45

S=29/45:2

S=29/90

Answer 3

S = (1/1.3 + 1/3.5 + ... + 1/7.9) + (1/2.4 + 1/4.6 + ... + 1/8.10)

S = 2(1/1 - 1/3 + 1/3 - 1/5 + ... + 1/7 - 1/9) + 1/2(1/2 - 1/4 + 1/4 - 1/6 + ... + 1/8 - 1/10) 

S = 2.(1 - 1/9) + 1/2.(1/2 - 1/10)

S = 16/9 + 1/5 = 89/45

Answer 4

Sai đấy.

2Ans=1-(1/3)+(1/2)-(1/4)+...+(1/8)-(1/10)

2Ans=(1+1/2+1/3+...+1/8)-(1/3+1/4+...+1/10)

2Ans=1+1/2-1/9-1/10

2Ans=58/45

Ans=29/45