Toán Giúp mình với: A=1/6+1/7+1/8+…..+1/20.Chứng tỏ rằng A>1 26/10/2021 By Liliana Giúp mình với: A=1/6+1/7+1/8+…..+1/20.Chứng tỏ rằng A>1
Xét tổng `1/6+1/7+1/8+1/9+1/10 > 1/10+1/10+1/10+1/10+1/10 = 1/21` Xét tổng `1/11+1/12+1/13+…+1/20 > 1/20+1/20+1/20+…+1/20 = 10.1/20=1/2` Vậy `A=1/6+1/7+1/8+…..+1/20 > 1/2+1/2=1` Trả lời
Xét tổng `1/6+1/7+1/8+1/9+1/10 > 1/10+1/10+1/10+1/10+1/10 = 1/21`
Xét tổng `1/11+1/12+1/13+…+1/20 > 1/20+1/20+1/20+…+1/20 = 10.1/20=1/2`
Vậy `A=1/6+1/7+1/8+…..+1/20 > 1/2+1/2=1`