Đáp án:
Giải thích các bước giải:
`A=1/4^2+1/6^2+1/8^2+...+1/160^2`
`=>A=1/16+1/6.6+1/8.8+...+1/160.160`
`=>A<1/16+1/4.6+1/6.8+...+1/158.160`
`=>2A<1/8+2/4.6+2/6.8+...+2/158.160`
`=>2A<1/8+1/4-1/6+1/6-1/8+...+1/158-1/160`
`=>2A<1/8+1/4-1/160`
`=>2A<1/8+39/160`
`=>2A<59/160`
`=>A<59/320<3/16`
`=>A<1/6`
`=>A>1/4.6+1/6.8+1/8.10+...+1/160.162`
`=>2A>2/4.6+2/6.8+2/8.10+...+2/160.162`
`=>2A>1/4-1/6+1/6-1/8+1/8-1/10+...+1/160-1/162`
`=>2A>1/4-1/162`
`=>A>1/8-1/2.162`
`=>A>1/8`
`=>1/8<A<3/16`
Vậy `1/8<A<3/16`.
