A = 1/31 + 1/32 + 1/33 + ... + 1/60
=> A = (1/31 + 1/32 + ... + 1/45) + (1/46 + 1/47 + ... 1/60) > (1/45) x 15 + (1/60) x 15
=> A > 1/3 + 1/4 = 7/12
Vậy A > 7/12 (đpcm)
cho \(A=\frac{1}{31}+\frac{1}{32}+\frac{1}{33}+...+\frac{1}{60}\)
chứng minh rằng \(A>\frac{7}{12}\)
A=1/31+1/32+1/33+...+1/60. chứng minh A>7/12
chưgs minh rằng :
1/31+1/32+1/33+.....+1/60>7/12
cho A = 1/31 + 1/32 + 1/33 + ... + 1/60 CMR : A > 7/12
chứng minh rằng A=1+3+31+32+33+34+.....+3102+3103chia hết cho 4
Cho:A=1/31+1/32+1/33+..............+1/60
Chứng minh rằngA>7/12
Cho C = 1 + 3 1 + 3 2 + 3 3 + . . . + 3 11 . Chứng minh rằng:
a) C ⋮ 13
b) C ⋮ 40
Cho C = 1 + 3 1 + 3 2 + 3 3 + . . . + 3 11 . Chứng minh rằng:
a, C ⋮ 13
b, C ⋮ 40
Chứng tỏ rằng
7/12<1/31+1/32+1/33+... +1/59+1/60<5/6
PLEASE, HELP ME