3C = 1+1/3 + .... + 1/3^59
3C - C = (1/3 - 1/3)+.....+(1/3^59 - 1/3^59) + 1 - 1/3^60
Vì 2C < 1 nên C < 1/2
3C = 1+1/3 + .... + 1/3^59
3C - C = (1/3 - 1/3)+.....+(1/3^59 - 1/3^59) + 1 - 1/3^60
Vì 2C < 1 nên C < 1/2
a,A=1/1^2+1/2^2+1/3^2+1/4^2+...+1/50^2.chung minh rang a<2
b;2^1+2^2+2^3+...+2^30.chung minh rang B chia het cho21
Cho S=1/3+1/3^2+1/3^3+...+1/3^2015 Chung minh rang s<1/2
cho C = 1 +3 + 32 + 33 + .... + 311 chung minh rang
a, chứng minh rằng C chia hết cho 13
b, chung minh rang C CHIA HET CHO 40
giai bai toan : chung minh rang : 1+1/2+1/3+1/4+..+1/32>3
hay chung minh rang A la so chinh phuong biet rang :A =1^3 + 2^3 + 3^3 + 4^3
Chung minh rang 1+3+3^2+3^3+...+3^11chia het cho 52
cho A=1/3^2-1/3^4+1/3^6-1/3^8+...+1/3^2014-1/3^2016 . Chung minh rang A < 0,1 . Hay tong quat bai toan
Minh dang can gap
Cho S= 3/1+3/11+3/12+3/13+3/14
Chung minh rang 1<S<2
chung minh rang
1/3 + 2/3^2 + ... + 100/3^100<3/4