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( ghi lại đề )
Ta có :
\(\frac{1}{4}z=\frac{2^{100}+1}{2^{100}+4}=\frac{2^{100}+4-3}{2^{100}+4}=\frac{2^{100}+4}{2^{100}+4}-\frac{3}{2^{100}+4}=1-\frac{3}{2^{100}+4}\)
\(\frac{1}{4}t=\frac{2^{102}+1}{2^{102}+4}=\frac{2^{102}+4-3}{2^{102}+4}=\frac{2^{102}+4}{2^{102}+4}-\frac{3}{2^{102}+4}=1-\frac{3}{2^{102}+4}\)
Lại có :
\(\frac{3}{2^{100}+4}>\frac{3}{2^{102}+4}\)
\(\Leftrightarrow\)\(-\frac{3}{2^{100}+4}< -\frac{3}{2^{102}+4}\)
\(\Leftrightarrow\)\(1-\frac{3}{2^{100}+4}< 1-\frac{3}{2^{102}+4}\)
\(\Leftrightarrow\)\(\frac{1}{4}z< \frac{1}{4}t\)
\(\Leftrightarrow\)\(z< t\)
Vậy \(z< t\)
Chúc bạn học tốt ~
ta có: \(T=\frac{2^{102}+1}{2^{100}+1}=\frac{2^2.\left(2^{100}+1\right)-3}{2^{100}+1}=\frac{2^2.\left(2^{100}+1\right)}{2^{100}+1}-\frac{3}{2^{100}+1}\)\(=4-\frac{3}{2^{100}+1}\)
\(Z=\frac{2^{100}+1}{2^{98}+1}=\frac{2^2.\left(2^{98}+1\right)-3}{2^{98}+1}=4-\frac{3}{2^{98}+1}\)
\(\Rightarrow\frac{3}{2^{100}+1}< \frac{3}{2^{98}+1}\)
\(\Rightarrow4-\frac{3}{2^{100}+1}>4-\frac{3}{2^{98}+1}\)
\(\Rightarrow T>Z\)
ta có: 298 < 2100
=> 298+1<2100+1
\(\Rightarrow\frac{2^{102}+1}{2^{98}+1}>\frac{2^{102}+1}{2^{100}+1}\)
Ta có A = \(\frac{10^{100}-1}{10^{98}-1}=\frac{10^{98}.10^2-10^2+99}{10^{98}-1}\)
\(=\frac{10^2\left(10^{98}-1\right)+99}{10^{98-1}}\)
\(=10^2+\frac{99}{10^{98}-1}\)
B= \(\frac{10^{101}-1}{10^{99}-1}=\frac{10^{99}.10^2-10^2+99}{10^{99}-1}\)
\(=\frac{10^2\left(10^{99}-1\right)+99}{10^{99}-1}\)
\(=10^2+\frac{99}{10^{99}-1}\)
Vì \(\frac{99}{10^{98}-1}>\frac{99}{10^{99}-1}\)nên \(10^2+\frac{99}{10^{98}-1}>10^2+\frac{99}{10^{99}-1}\)=> A > B
Vậy A > B
Bài làm:
Xét: \(\frac{1}{5^2}>\frac{1}{5.6}\) ; \(\frac{1}{6^2}>\frac{1}{6.7}\) ; ... ; \(\frac{1}{100^2}>\frac{1}{100.101}\)
=> \(A>\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{100.101}\)
\(=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{100}-\frac{1}{101}\)
\(=\frac{1}{5}-\frac{1}{101}=\frac{96}{505}>\frac{1}{6}\) (1)
Lại có: \(\frac{1}{5^2}< \frac{1}{4.5}\) ; \(\frac{1}{6^2}< \frac{1}{5.6}\) ; ... ; \(\frac{1}{100^2}< \frac{1}{99.100}\)
=> \(A< \frac{1}{4.5}+\frac{1}{5.6}+...+\frac{1}{99.100}\)
\(=\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{99}-\frac{1}{100}\)
\(=\frac{1}{4}-\frac{1}{100}< \frac{1}{4}\) (2)
Từ (1) và (2) => \(\frac{1}{6}< A< \frac{1}{4}\)
ĐẶT : \(A=1+\frac{1}{2}+\frac{1}{3}+....+\frac{1}{100}\)
TA ĐỔI : \(A=2-1+1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+....+\frac{1}{99}-\frac{1}{100}\)
\(A=2-1-\frac{1}{100}\)
\(A=\frac{200}{100}-\frac{100}{100}-\frac{1}{100}\)
\(A=\frac{99}{100}\)
ĐÁP ÁN ĐÂY, XIN LỖI VÌ MH KO THỂ GIẢI RÕ HƠN
~HOK TỐT~
Ta có : \(N=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{1000.1001}\)
\(=\frac{2-1}{1.2}+\frac{3-2}{2.3}+\frac{4-3}{3.4}+...+\frac{1001-1000}{1000.1001}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{1000}-\frac{1}{1001}\)
\(=1-\frac{1}{1001}=\frac{1000}{1001}\)
Ta thấy : \(1001< 2020\Rightarrow\frac{1}{1001}>\frac{1}{2020}\)
\(\Rightarrow-\frac{1}{1001}< -\frac{1}{2020}\)
\(\Rightarrow1-\frac{1}{1001}< 1-\frac{1}{2020}\Rightarrow\frac{1000}{1001}< \frac{2019}{2020}\)
Hay : \(N< M\)
Câu 1 :
Ta có : \(A=\frac{10^{100}+1}{10^{101}+1}\)
\(\Rightarrow10A=\frac{10^{101}+10}{10^{101}+1}=\frac{10^{101}+1+9}{10^{101}+1}=1+\frac{9}{10^{101}+1}\)
Ta có : \(B=\frac{10^{101}+1}{10^{102}+1}\)
\(10B=\frac{10^{102}+10}{10^{102}+1}=\frac{10^{102}+1+9}{10^{102}+1}=1+\frac{9}{10^{102}+1}\)
Vì 10101+1<10102+1
\(\Rightarrow\frac{9}{10^{101}+1}>\frac{9}{10^{102}+1}\)
\(\Rightarrow1+\frac{9}{10^{101}+1}>1+\frac{9}{10^{102}+1}\)
\(\Rightarrow\)10A>10B
\(\Rightarrow\)A>B
Vậy A>B.
Câu 2 :
Ta có : \(E=\frac{2000+2001}{2001+2002}=\frac{2000}{2001+2002}+\frac{2001}{2001+2002}\)
Vì 2001<2001+2002 và 2002<2001+2002
\(\Rightarrow\hept{\begin{cases}\frac{2000}{2001}>\frac{2000}{2001+2002}\\\frac{2001}{2002}>\frac{2001}{2001+2002}\end{cases}}\)
\(\Rightarrow C>E\)
Vậy C>E.
\(P=\frac{1}{1^2}+\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{2019^2}< 1+\frac{1}{2^2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2018.2019}\)
\(P< 1+\frac{1}{4}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2018}-\frac{1}{2019}=\frac{7}{4}-\frac{1}{2019}< \frac{7}{4}\)
ta có \(A=\frac{1}{100}+\frac{1}{101}+...+\frac{1}{149}\)
ta thấy \(\frac{1}{100}=\frac{1}{100}\)
\(\frac{1}{101}<\frac{1}{100}\)
\(\frac{1}{102}<\frac{1}{100}\)
................................
\(\frac{1}{149}<\frac{1}{100}\)
\(\Rightarrow A=\frac{1}{100}+\frac{1}{101}+\frac{1}{102}+...+\frac{1}{149}<\frac{1}{100}+\frac{1}{100}+\frac{1}{100}+...+\frac{1}{100}\)
\(=\frac{49}{100}<\frac{1}{2}\)
vì \(A<\frac{49}{100}<\frac{1}{2}\Leftrightarrow A<\frac{1}{2}\)