1. Chứng minh rằng : 1/5 +1/14 +1/28 +1/44 +1/61+ 1/85 +1/91 < 1/2
2. Chứng tỏ rằng : 1/5+1/6+1/7+...+1/16+1/17 < 2
3. Tính: A= [878787/9595953+ (-8787/9595)] * 1234621/5678765
4. So sánh : 10^8+2/10^8-1 ; B= 10^8/10^8-3
chứng minh rằng 1/5+1/14+1/28+1/44+1/61+1/85+1/91<1/2
Chứng minh rằng : 1/5 + 1/14 + 1/28 + 1/44 + 1/61 + 1/85 + 1/91 < 1/2
1/97 chứ sao lại 1/91!
giải:
đặt :1/5+1/14+1/28+1/44+1/61+1/85+1/97 =A
ta có :A=1/5(1/14+1/28+1/44)+(1/61+1/85+1/97)
A<1/5(1/14.3)+(1/61.3)
A<1/5+3/14+3/61
A<1/5+3/12+1/20
A<1/5+1/4+1/20
=>A<1/2
VẬY dpcm
chứng minh rằng 1/5+1/14+1/28+1/44+1/61+1/85+1/91<1/2
chứng tỏ rằng
A= 1/5 + 1/14 + 1/28 + 1/44 + 1/61 + 1/85 + 1/97 < 1/2
Ta có \(\frac{1}{5}=\frac{1}{5}\)
\(\frac{1}{14}< \frac{1}{10};\frac{1}{28}< \frac{1}{10}\)
\(\frac{1}{44}< \frac{1}{40};\frac{1}{61}< \frac{1}{40};\frac{1}{85}< \frac{1}{40};\frac{1}{97}< \frac{1}{40}\)
\(\Rightarrow\frac{1}{5}+\frac{1}{14}+\frac{1}{28}+\frac{1}{44}+\frac{1}{61}+\frac{1}{85}+\frac{1}{97}< \frac{1}{5}+\frac{1}{10}+\frac{1}{10}+\frac{1}{40}+\frac{1}{40}+\frac{1}{40}+\frac{1}{40}=\frac{1}{5}+\frac{1}{5}+\frac{1}{10}=\frac{5}{10}=\frac{1}{2}\)\(\Rightarrow A< \frac{1}{2}\)
Chứng minh rằng : 1/5 + 1/14 + 1/28 + 1/44 + 1/61 + 1/85 < 1/2
Đặt A=15+114+128+144+161+185+197
Ta có:
A=15+(114+128+144)+(161+185+197)
A<15(114.3)+(161.3)
A<15+314+361
A<15+312+120
A<15+14+120
⇒A<12
Vậy 15+
ứng tỏ rằng 1/5 +1/14 + 1/28 + 1/44 +1/61 + 1 / 85 + 1 / 91 < 1/2
ta có vế trái=0,37 mà 1/2=0,5 nên suy ra nó lớn hơn:v
1) Chứng tỏ
1/4^2 + 1/5^2 + 1/6^2 + .... + 1/64^2 < 5/16
2) Chứng tỏ
A= 1/5 + 1/14 + 1/28 + 1/44 + 1/61 + 1/85 + 1/97 < 1/2
Chứng minh rằng:
\(\frac{1}{5}+\frac{1}{14}+\frac{1}{28}+\frac{1}{44}+\frac{1}{61}+\frac{1}{85}+\frac{1}{91}<\frac{1}{2}\)
chứng tở rằng 1 + 1/2 + 1/3 + 1/4 + 1/5 + 1/6 + 1/7 + 1/8 + 1/9 + 1/10 + 1/11 + 1/12 + 1/13 + 1/14 + 1/15 + 1/16 + 1/17 + 1/18 + 1/ 19 + 1/20 + 1/21 + 1/22 + 1/ 23 + 1/24 + 1/25 + 1/26 + 1/27 + 1/28 + 1/29 + 1/30 + 1/31 + 1/32 < 3
ta có
1/2<1/1.2
1/3<1/2.3
...
1/32<1/31.32
=>1/2+1/3+...+1/32<1/1.2+1/2.3+...+1/31.32
=>1/2+1/3+...+1/32<1/1-1/2+1/2-1/3+...+1/31-1/32
=>1/2+1/3+...+1/32<1/1-1/32=31/32
vì 31/32<1
=>tổng đó <1
ta lại có 1+1=2 mà 2 <3
=>tổng đó <3
vậy:-------(bn tự lm nha)
k cho mik vs nha