S=3/(1×4) + 3/(4×7)+3/(7×10)+3/(10×13)+3/(13×16) S=1/(1×2)+1/(2×3)+1/(3×4)+...+1/49×50

Đáp án:

`S=3/(1.4)+3/(4.7)+3/(7.10)+3/(10.13)+3/(13.16)`

`S=1/1.4+1/4.7+1/7.10+1/10.13+1/13.16`

`S=1-1/4+1/4-1/7+1/7-1/10+1/10-1/13+1/13-1/16`

`S=1-1/16`

`S=15/16`

`-------------`

`S=1/(1.2)+1/(2.3)+1/(3.4)+...+1/49.50`

`S=1-1/2+1/2-1/3+1/3-1/4+...+1/49-1/50`

`S=1-1/50`

`S=49/50`

Đáp án:

Giải thích các bước giải:

`\bb S=3/(1 xx 4) + 3/(4 xx 7)+3/(7 xx 10)+3/(10xx 13)+3/(13xx16)`

`\bb S= 1/1 - 1/4 + 1/4- 1/7 + 1/7- 1/10+ 1/10-1/13 + 1/13 - 1/16`

`\bb S = 1/1 - 1/16`

`\bb S = 15/16`

_____________________________________________________

`\bb S=1/(1 xx 2)+1/(2 xx 3)+1/(3 xx 4)+...+1/(49 xx 50)`

`\bb S = 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/49 - 1/50`

`\bb S = 1 - 1/50`

`\bb S = 49/50`