Ta có
1/31 + 1/32 + ... + 1/40 < 1/31 + 1/31 +... + 1/31 = 1/31x10
1/41 + 1/42 + ... + 1/50 < 1/41 + 1/41 + ... + 1/41 = 1/41x10
1/51 + 1/52 + ... + 1/60 < 1/51 + 1/51 + ... + 1/51 = 1/51x10
=> A < 1/31 x 10 + 1/41 x 10 + 1/51 x 10
=> A < 1/30 x 10 + 1/40 x 10 + 1/50 x 10
=> A < 1/3 + 1/4 + 1/5 = 47/60 < 48/60 = 4/5
=> A < 4/5 (ĐPCM)
cho mình 1 like nhé
cho A= 1/31+1/32+1/33+...+1/60
chứng minh 3/5<A<4/5
A=1/31+1/32+1/33+...+1/60. chứng minh A>7/12
chung minh bat dang thuc S=1/31+1/32+1/33+...+1/60.CMR3/4<S<4/5.tra loi nhanh ho minh nha
a, tính a= 2/1.3+2/3.5+2/5.7+2/7.9+...+2/2017.2019
b, cho S= 1/31+1/32+1/33...+1/60. chứng minh S<4/5
chú ý / là phần
cho A= 1/31+1/32+1/33+.....+1/60
chứng minh rằng A> 7/12
Cho S = 1/31+1/32+1/33+.......+1/60.Chứng minh 3/5 < S < 4/
Chứng minh rằng: S= 1/31+1/32+1/33+...+1/60<4/5
Chứng minh rằng
\(A=\frac{3}{5}< \frac{1}{31}+\frac{1}{32}+\frac{1}{33}+...+\frac{1}{60}< \frac{4}{5}\)
Cho A =\(\frac{1}{31}+\frac{1}{32}+\frac{1}{33}+...+\frac{1}{59}+\frac{1}{60}\) Chứng minh rằng A<\(\frac{4}{5}\)