a, so sánh: \(\sqrt{17}+\sqrt{26}+1\)và \(\sqrt{99}\)
b, CMR: \(\frac{1}{\sqrt{1}}+\frac{1}{\sqrt{2}}+...+\frac{1}{\sqrt{100}}\)>10
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1 tháng 3 2020
a)Ta có:\(\sqrt{17}>\sqrt{16}\)
\(\sqrt{26}>\sqrt{25}\)
\(\implies\) \(\sqrt{17}+\sqrt{26}>\sqrt{16}+\sqrt{25}\)
\(\implies\) \(\sqrt{17}+\sqrt{26}+1>\sqrt{16}+\sqrt{25}+1=4+5+1=10\)
Mà \(\sqrt{100}=10\) \(\implies\) \(\sqrt{17}+\sqrt{26}+1>\sqrt{100}\)
Mà \(\sqrt{100}>\sqrt{99}\) \(\implies\) \(\sqrt{17}+\sqrt{26}+1>\sqrt{99}\)
b)Ta có:\(\frac{1}{\sqrt{1}}+\frac{1}{\sqrt{2}}+....+\frac{1}{\sqrt{100}}>\frac{1}{\sqrt{100}}+\frac{1}{\sqrt{100}}+...+\frac{1}{\sqrt{100}}=100.\frac{1}{\sqrt{100}}\)
\(\implies\) \(\frac{1}{\sqrt{1}}+\frac{1}{\sqrt{2}}+....+\frac{1}{\sqrt{100}}>\frac{1}{10}.100=10\)
\(\implies\) \(\frac{1}{\sqrt{1}}+\frac{1}{\sqrt{2}}+....+\frac{1}{\sqrt{100}}>10\left(đpcm\right)\)
HH
13 tháng 2 2018
a) Ta có \(\sqrt{17}\)>\(\sqrt{16}\)
\(\sqrt{26}\)>\(\sqrt{25}\)
=>\(\sqrt{17}\)+\(\sqrt{26}\)+1>\(\sqrt{16}\)+\(\sqrt{25}\)+1
=>\(\sqrt{17}\)+\(\sqrt{26}\)+1> 4+ 5 +1
=>\(\sqrt{17}\)+\(\sqrt{26}\)+1 >10 hay >\(\sqrt{100}\)
=>\(\sqrt{17}\)+\(\sqrt{26}\)+1>\(\sqrt{99}\)
b) \(\frac{1}{\sqrt{1}}\)=1 >\(\frac{1}{10}\)
\(\frac{1}{\sqrt{2}}\)>\(\frac{1}{\sqrt{100}}\)=\(\frac{1}{10}\)
....................................
\(\frac{1}{\sqrt{100}}\)=\(\frac{1}{10}\)
=>\(\frac{1}{\sqrt{1}}\)+\(\frac{1}{\sqrt{2}}\)+\(\frac{1}{\sqrt{3}}\)+...+\(\frac{1}{\sqrt{100}}\)>\(\frac{1}{10}\)+\(\frac{1}{10}\)+...+\(\frac{1}{10}\)(có 100 số \(\frac{1}{10}\))
=>\(\frac{1}{\sqrt{1}}\)+\(\frac{1}{\sqrt{2}}\)+\(\frac{1}{\sqrt{3}}\)+...+\(\frac{1}{\sqrt{100}}\)> \(\frac{100}{10}\)=10
3 tháng 4 2018
\(a)\) Ta có :
\(\sqrt{17}+\sqrt{26}+1>\sqrt{16}+\sqrt{25}+1=4+5+1=10=\sqrt{100}>\sqrt{99}\)
Vậy \(\sqrt{17}+\sqrt{26}+1>\sqrt{99}\)
Chúc bạn học tốt ~
NT
26 tháng 10 2016
1/√1 > 1/10
1/√2 > 1/10
1/√3 > 1/10
....................
1/√99 > 1/10
1/√100 = 1/10
Cộng từng vế ta có:
1/√1 + 1/√2 + 1/√3 + ... + 1/√100 >100.1/0 = 10 (Đpcm)
2 tháng 2 2017
\(\sqrt{17}+\sqrt{26}+1>\sqrt{16}+\sqrt{25}+1=4+5+1=10=\sqrt{100}>\sqrt{99}\)
3 tháng 11 2015
a)\(\sqrt{17}+\sqrt{26}+1>\sqrt{16}+\sqrt{25}+1=4+5+1=10\)
b) \(\frac{1}{\sqrt{1}}+\frac{1}{\sqrt{2}}+\frac{1}{\sqrt{3}}+.....+\frac{1}{\sqrt{100}}>\frac{1}{\sqrt{100}}+\frac{1}{\sqrt{100}}+\frac{1}{\sqrt{100}}+.......+\frac{1}{\sqrt{100}}=\frac{100}{\sqrt{100}}=10\)
12 tháng 11 2017
a,\(\sqrt{17}+\sqrt{26}+1>\sqrt{16}+\sqrt{25}+1=10=\sqrt{100}>\sqrt{99}\)
b,Ta có:\(\hept{\begin{cases}\frac{1}{\sqrt{1}}>\frac{1}{\sqrt{100}}\\\frac{1}{\sqrt{2}}>\frac{1}{\sqrt{100}}\\.........\end{cases}}\)\(\Rightarrow\frac{1}{\sqrt{1}}+\frac{1}{\sqrt{2}}+........+\frac{1}{\sqrt{100}}>\frac{1}{\sqrt{100}}+\frac{1}{\sqrt{100}}+......+\frac{1}{\sqrt{100}}=\frac{100}{\sqrt{100}}=10\)
23 tháng 7 2016
mình chỉ giải được phần này thôi
b.A = \(\sqrt{17}\)+\(\sqrt{26}\)+ 1 > \(\sqrt{16}\)+\(\sqrt{25}\)+ 1 = 4 + 5 +1 = 10
B = \(\sqrt{99}\)<\(\sqrt{100}\)= 10
=> A > B
B
28 tháng 7 2019
\(a,A=\frac{1}{\sqrt{1}+\sqrt{2}}+\frac{1}{\sqrt{2}+\sqrt{3}}+..+\frac{1}{\sqrt{99}+\sqrt{100}}\)
\(=\frac{\sqrt{1}-\sqrt{2}}{1-2}+\frac{\sqrt{2}-\sqrt{3}}{2-3}+...+\frac{\sqrt{99}-\sqrt{100}}{99-100}\)
\(=\frac{1-\sqrt{2}+\sqrt{2}-\sqrt{3}+...+\sqrt{99}-\sqrt{100}}{-1}\)
\(=\frac{1-\sqrt{100}}{-1}=9\)
\(b,B=\frac{1}{\sqrt{1}}+\frac{1}{\sqrt{2}}+\frac{1}{\sqrt{3}}+..+\frac{1}{\sqrt{99}}\)
\(=\frac{2}{\sqrt{1}+\sqrt{1}}+\frac{2}{\sqrt{2}+\sqrt{2}}+\frac{2}{\sqrt{3}+\sqrt{3}}+...+\frac{2}{\sqrt{99}+\sqrt{99}}>\frac{2}{\sqrt{1}+\sqrt{2}}+\frac{2}{\sqrt{2}+\sqrt{3}}+...+\frac{2}{\sqrt{99}+\sqrt{100}}\)\(\Rightarrow B>2\left(\frac{1}{\sqrt{1}+\sqrt{2}}+\frac{1}{\sqrt{2}+\sqrt{3}}+..+\frac{1}{\sqrt{99}+\sqrt{100}}\right)\)
\(\Rightarrow B>2\left(\frac{\sqrt{1}-\sqrt{2}+\sqrt{2}-\sqrt{3}+...+\sqrt{99}-\sqrt{100}}{-1}\right)\)
\(\Rightarrow B>2\left(\frac{1-\sqrt{100}}{-1}\right)\)
\(\Rightarrow B>2.9=18\left(ĐPCM\right)\)
a) \(\sqrt{17}>\sqrt{16}=4\); \(\sqrt{26}>\sqrt{25}=5\) => \(\sqrt{17}+\sqrt{26}+1>4+5+1=10=\sqrt{100}>\sqrt{99}\)
Vậy \(\sqrt{17}+\sqrt{26}+1>\sqrt{99}\)
b) \(\frac{1}{\sqrt{1}}>\frac{1}{\sqrt{100}};\frac{1}{\sqrt{2}}>\frac{1}{\sqrt{100}};...;\frac{1}{\sqrt{99}}>\frac{1}{\sqrt{100}}\)
=> \(\frac{1}{\sqrt{1}}+\frac{1}{\sqrt{2}}+...+\frac{1}{\sqrt{100}}>\frac{1}{\sqrt{100}}+\frac{1}{\sqrt{100}}+...+\frac{1}{\sqrt{100}}=\frac{100}{\sqrt{100}}=10\)
Vậy.....