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6 tháng 4 2023
`a,`
`5/6=1-1/6`
`7/8=1-1/8`
Mà `1/6>1/8 -> 5/6<7/8`
`b,`
`9/5=(9 \times 2)/(5 \times 2)=18/10`
`3/2=(3 \times 5)/(2 \times 5)=15/10`
`18/10 > 15/10 -> 9/5 > 3/2`
`c,`
`2017/2018 = 1-1/2018`
`2019/2020=1-1/2020`
`1/2018 > 1/2020 -> 2017/2018 < 2019/2020`
`d,`
`2018/2017 = 1+1/2017`
`2020/2019 = 1+1/2019`
`1/2017 > 1/2019 -> 2018/2017>2020/2019`
TK
6
T
6 tháng 6 2019
#)Giải :
Ta có : \(A=\frac{2017}{2018}+\frac{2018}{2019}+\frac{2019}{2019}< 1+1+1\)
\(\Rightarrow A< 3\)
Mình giải thế này cho ngắn gọn, với lại nhanh ^^
T
8 tháng 6 2019
#)Giải :
\(Q=2+\frac{2016}{2017+2018+2019}+\frac{2017}{2017+2018+2019}+\frac{2018}{2017+2018+2019}\)
Ta thấy : \(2>\frac{2016}{2017};2>\frac{2017}{2018};2>\frac{2018}{2019}\left(1\right)\)
\(\frac{2016}{2017+2018+2019}< \frac{2016}{2017}\left(2\right)\)
\(\frac{2017}{2017+2018+2019}< \frac{2017}{2018}\left(3\right)\)
\(\frac{2018}{2017+2018+2019}< \frac{2018}{2019}\left(4\right)\)
Từ (1) (2) (3) (4) \(\Rightarrow P>Q\)
ND
2
DL
15 tháng 7 2018
\(A=\frac{2016}{2017}+\frac{2017}{2018}+\frac{2018}{2019}=\left(1-\frac{1}{2017}\right)+\left(1-\frac{1}{2018}\right)+\left(1-\frac{1}{2019}\right)\)
\(A=3-\left(\frac{1}{2017}+\frac{1}{2018}+\frac{1}{2019}\right)< 3\)
15 tháng 7 2018
Ta có :
2016/2017 < 1
2017/2018 < 1
2018/2019 < 1
Mà 2016/2017 + 2017/2018 + 2018/2019 < 1 + 1 + 1 = 3
Nên A < 3
ND
3
15 tháng 7 2018
\(A=\frac{2016}{2017}+\frac{2017}{2018}+\frac{2018}{2019}\)
Ta có:
\(\frac{2016}{2017}< 1\)
\(\frac{2017}{2018}< 1\)
\(\frac{2018}{2019}< 1\)
\(\Rightarrow\frac{2016}{2017}+\frac{2017}{2018}+\frac{2018}{2019}< 1+1+1=3\)
\(\Rightarrow A< 3\)
Vậy \(A< 3\)
Tham khảo nhé
15 tháng 7 2018
\(\frac{2016}{2017}+\frac{2017}{2018}+\frac{2018}{2019}\)
\(=1-\frac{1}{2017}+1-\frac{1}{2018}+1-\frac{1}{2019}\)
\(=\left(1+1+1\right)-\left(\frac{1}{2017}+\frac{1}{2018}+\frac{1}{2019}\right)\)
\(=3-\left(\frac{1}{2017}+\frac{1}{2018}+\frac{1}{2019}\right)< 3\)
Vậy \(\frac{2016}{2017}+\frac{2017}{2018}+\frac{2018}{2019}< 3\left(đpcm\right)\)
PN
6
25 tháng 6 2018
a) \(\frac{1995}{1997}\)và \(\frac{1995}{1996}\)
Ta có : \(\frac{1995}{1996}=\frac{1995\times2}{1996\times2}=\frac{3990}{3992}\)
\(1-\frac{1995}{1997}=\frac{2}{1997};1-\frac{3990}{3992}=\frac{2}{3992}\)
Vì \(\frac{2}{1997}>\frac{2}{3992}\)nên \(\frac{1995}{1997}< \frac{3990}{3992}\)hay \(\frac{1995}{1997}< \frac{1995}{1996}\).
b) \(\frac{2016}{2017}\)và \(\frac{2017}{2018}\)
Ta có : \(1-\frac{2016}{2017}=\frac{1}{2017};1-\frac{2017}{2018}=\frac{1}{2018}\)
Vì \(\frac{1}{2017}>\frac{1}{2018}\)nên \(\frac{2016}{2017}< \frac{2017}{2018}\).
c) \(\frac{2018}{2019}\)và \(\frac{2017}{2016}\).
Vì \(\frac{2018}{2019}< 1;1< \frac{2017}{2016}\)nên \(\frac{2018}{2019}< \frac{2017}{2016}\).
~ HOK TỐT ~
DL
11 tháng 6 2018
Bài 1:
Ta có:
\(N=\frac{2017+2018}{2018+2019}=\frac{2017}{2018+2019}+\frac{2018}{2018+2019}\)
Do \(\hept{\begin{cases}\frac{2017}{2018+2019}< \frac{2017}{2018}\\\frac{2018}{2018+2019}< \frac{2018}{2019}\end{cases}\Rightarrow\frac{2017}{2018+2019}+\frac{2018}{2018+2019}< \frac{2017}{2018}+\frac{2018}{2019}}\)
\(\Leftrightarrow N< M\)
Vậy \(M>N.\)
Bài 2:
Ta có:
\(A=\frac{2017}{987653421}+\frac{2018}{24681357}=\frac{2017}{987654321}+\frac{2017}{24681357}+\frac{1}{24681357}\)
\(B=\frac{2018}{987654321}+\frac{2017}{24681357}=\frac{1}{987654321}+\frac{2017}{987654321}+\frac{2017}{24681357}\)
Do \(\hept{\begin{cases}\frac{2017}{987654321}+\frac{2017}{24681357}=\frac{2017}{987654321}+\frac{2017}{24681357}\\\frac{1}{24681357}>\frac{1}{987654321}\end{cases}}\)
\(\Rightarrow\frac{2017}{987654321}+\frac{2017}{24681357}+\frac{1}{24681357}>\frac{1}{987654321}+\frac{2017}{987654321}+\frac{2017}{24681357}\)
\(\Leftrightarrow A>B\)
Vậy \(A>B.\)
Bài 3:
\(\frac{2016}{2017}+\frac{2017}{2018}+\frac{2018}{2019}+\frac{2019}{2016}=1-\frac{1}{2017}+1-\frac{1}{2018}+1-\frac{1}{2019}+1+\frac{3}{2016}\)
\(=1+1+1+1-\frac{1}{2017}-\frac{1}{2018}-\frac{1}{2019}+\frac{3}{2016}\)
\(=4-\left(\frac{1}{2017}+\frac{1}{2018}+\frac{1}{2019}-\frac{3}{2016}\right)\)
Do \(\hept{\begin{cases}\frac{1}{2017}< \frac{1}{2016}\\\frac{1}{2018}< \frac{1}{2016}\\\frac{1}{2019}< \frac{1}{2016}\end{cases}\Rightarrow\frac{1}{2017}+\frac{1}{2018}+\frac{1}{2019}< \frac{1}{2016}+\frac{1}{2016}+\frac{1}{2016}=\frac{3}{2016}}\)
\(\Rightarrow\frac{1}{2017}+\frac{1}{2018}+\frac{1}{2019}-\frac{3}{2016}\)âm
\(\Rightarrow4-\left(\frac{1}{2017}+\frac{1}{2018}+\frac{1}{2019}-\frac{3}{2016}\right)>4\)
Vậy \(\frac{2016}{2017}+\frac{2017}{2018}+\frac{2018}{2019}+\frac{2019}{2016}>4.\)
Bài 4:
\(\frac{1991.1999}{1995.1995}=\frac{1991.\left(1995+4\right)}{\left(1991+4\right).1995}=\frac{1991.1995+1991.4}{1991.1995+4.1995}\)
Do \(\hept{\begin{cases}1991.1995=1991.1995\\1991.4< 1995.4\end{cases}}\Rightarrow1991.1995+1991.4< 1991.1995+1995.4\)
\(\Rightarrow\frac{1991.1995+1991.4}{1991.1995+4.1995}< \frac{1991.1995+1995.4}{1991.1995+4.1995}=1\)
\(\Rightarrow\frac{1991.1999}{1995.1995}< 1\)
Vậy \(\frac{1991.1999}{1995.1995}< 1.\)
14 tháng 7 2019
Ta có:
\(1-\frac{2017}{2018}=\frac{1}{2018};1-\frac{2018}{2019}=\frac{1}{2019};1-\frac{2019}{2020}=\frac{1}{2020}\)
Vì \(\frac{1}{2018}>\frac{1}{2019}>\frac{1}{2020}\)nên \(\frac{2017}{2018}< \frac{2018}{2019}< \frac{2019}{2020}\)
14 tháng 7 2019
2017/2018 = (2018-1)/2018 = 1-1/2018
2018/2019 = (2019-1)/2019 = 1 - 1/2019
2019/2020 = (2020-1)/2020 = 1 - 1/2020
Có 1/2018 > 1/2019 > 1/2020 => 2017/2018 < 2018/2019 < 2019/2020
DN
2
NI
3 tháng 10 2021
Phân tích 2 phân số ta có:
1 = \(\dfrac{2017\times2019}{2017\times2019}\) = \(\dfrac{\left(2018-1\right)\times\left(2018+1\right)}{2017\times2019}\) = \(\dfrac{2018^2-1^2}{2017\times2019}\)
\(\dfrac{2018\times2018}{2017\times2019}\) = \(\dfrac{2018^2}{2017\times2019}\)
Vì \(2018^2\) > \(2018^2-1^2\) nên \(\dfrac{2018^2}{2017\times2019}\) > \(\dfrac{2018^2-1^2}{2017\times2019}\) hay \(\dfrac{2018\times2018}{2017\times2019}\) > 1
(Áp dụng hằng đẳng thức \(a^2-b^2\) = (a - b)(a + b))
3 tháng 10 2021
nhầm dòng 2 nhé
\(=\dfrac{2018\times2018}{2018\times2018-1}=\)
Vì \(2018\times2018>2018\times2018-1\) nên \(\dfrac{2018\times2018}{2018\times2018-1}>1\)