Toán Cho A= 1/31 + 1/32 + 1/33+ …+ 1/60 Cmr 3/5< A< 4/5 08/09/2021 By Hailey Cho A= 1/31 + 1/32 + 1/33+ …+ 1/60 Cmr 3/5< A< 4/5
ta có: 1/32 <1/31<1/30 1/33<1/32<1/31 : : 1/61<1/60<1/59 ___________________________________________________________________________________________ 1/32+1/33+1/34+…+1/66<1/31+1/32+1/33+…+1/60<1/30+1/31+1/32+…+1/59 3/5 < 1/31+1/32+1/33+…+1/60< 4/5 => 3/5< A<4/5 Trả lời
ta có: 1/32 <1/31<1/30 1/33<1/32<1/31 : : 1/61<1/60<1/59
___________________________________________________________________________________________
1/32+1/33+1/34+…+1/66<1/31+1/32+1/33+…+1/60<1/30+1/31+1/32+…+1/59
3/5 < 1/31+1/32+1/33+…+1/60< 4/5
=> 3/5< A<4/5