M= (1/41+.....+1/60)+(1/61+.......+1/80)
SUY RA
M>1/60*20+1/80*20=1/3+1/4=7/12
VẬY M>7/12
M= (1/41+.....+1/60)+(1/61+.......+1/80)
SUY RA
M>1/60*20+1/80*20=1/3+1/4=7/12
VẬY M>7/12
Chứng tỏ rằng : 7/12 <1/41 +1/42 + 1/43 + 1/44 + ..... +1/79 +1/80 <1
Hãy chứng tỏ rằng
\(\frac{7}{12}< \frac{1}{41}+\frac{1}{42}+...+\frac{1}{79}+\frac{1}{80}< 1\)\(1\)
Hãy chứng tỏ rằng:
\(\frac{7}{12}\)<\(\frac{1}{41}+\frac{1}{42}+\frac{1}{43}+............+\frac{1}{79}+\frac{1}{80}< 1\)
Chứng minh:7/12< 1/41+1/42+1/43+...+1/79+1/80<1
ĐỀ BÀI: (Chia đôi dãy phân số rồi so sánh)Chứng tỏ rằng
7/12<1/41+1/42+1/43+...+1/79+ 1/80<5/6
P/S: / là phân số nhé!!!
Chứng tỏ rằng:7/12<1/41+1/42+1/43+...+1/89+1/90<1
Cho A = 1/41 + 1/42 + 1/43 + .............+ 1/80. Chứng minh A > 1/2
chung to A bang 1/41+1/42+1/43+...+1/80>7/12
S=1/41+1/42+1/43+.....+1/80
Chung to S>7/12