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Có \(A=\frac{10^{2017}+1-3}{10^{2017}+1}=1-\frac{3}{10^{2017}+1}\)
\(B=\frac{10^{2017}+3-3}{10^{2017}+3}=1-\frac{3}{10^{2017}+3}\)
Có 102017+1<102017+3
=> \(\frac{3}{10^{2017}+1}>\frac{3}{10^{2017}+3}\)
=>A<B
c) E = \(\dfrac{4116-14}{10290-35}\) và K = \(\dfrac{2929-101}{2.1919+404}\)
E = \(\dfrac{4116-14}{10290-35}\)
E = \(\dfrac{14.\left(294-1\right)}{35.\left(294-1\right)}\)
E = \(\dfrac{14}{35}\)
K = \(\dfrac{2929-101}{2.1919+404}\)
K = \(\dfrac{101.\left(29-1\right)}{101.\left(38+4\right)}\)
K = \(\dfrac{29-1}{34+8}\)
K = \(\dfrac{28}{42}\) = \(\dfrac{2}{3}\)
Ta có : E = \(\dfrac{14}{35}\) và K = \(\dfrac{2}{3}\)
\(\dfrac{14}{35}\) = \(\dfrac{42}{105}\)
\(\dfrac{2}{3}\) = \(\dfrac{70}{105}\)
Vậy E < K
Các câu còn lại tương tự
Sửa đề: \(C=1+3^1+3^2+...+3^{100}\)
b) Ta có: \(C=1+3^1+3^2+...+3^{100}\)
\(\Leftrightarrow3\cdot C=3+3^2+...+3^{101}\)
\(\Leftrightarrow C-3\cdot C=1+3+3^2+...+3^{100}-3-3^2-...-3^{100}-3^{101}\)
\(\Leftrightarrow-2\cdot C=1-3^{101}\)
hay \(C=\dfrac{3^{101}-1}{2}\)
b) Ta có: C=1+31+32+...+3100C=1+31+32+...+3100
⇔3⋅C=3+32+...+3101⇔3⋅C=3+32+...+3101
⇔C−3⋅C=1+3+32+...+3100−3−32−...−3100−3101⇔C−3⋅C=1+3+32+...+3100−3−32−...−3100−3101
⇔−2⋅C=1−3101
\(\Leftrightarrow2\left(\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+...+\dfrac{1}{x\left(x+1\right)}\right)=\dfrac{2015}{2017}\)
\(\Leftrightarrow\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{x}-\dfrac{1}{x+1}=\dfrac{2015}{4034}\)
\(\Leftrightarrow\dfrac{1}{2}-\dfrac{1}{x+1}=\dfrac{2015}{4034}\)
\(\Leftrightarrow\dfrac{1}{x+1}=\dfrac{1}{2017}\)
=>x+1=2017
hay x=2016
Ta có:
\(\frac{2017^{10}+1}{2017^{10}-1}=1+\frac{2}{2017^{10}-1}\)
Lại có:
\(\frac{2017^{10}-1}{2017^{10}-3}=1+\frac{2}{2017^{10}-3}\)
Vì \(1+\frac{2}{2017^{10}-1}< 1+\frac{2}{2017^{10}-3}\)
Nên \(\frac{2017^{10}+1}{2017^{10}-1}< \frac{2017^{10}-1}{2017^{10}-3}\)
Vậy \(\frac{2017^{10}+1}{2017^{10}-1}< \frac{2017^{10}-1}{2017^{10}-3}\)
Ta có
\(\frac{2017^{10}+1}{2017^{10}-1}=\frac{2017^{10}-1+2}{2017^{10}-1}=1+\frac{2}{2017^{10}-1}\)
\(\frac{2017^{10}-1}{2017^{10}-3}=\frac{2017^{10}-3+2}{2017^{10}-3}=1+\frac{2}{2017^{10}-3}\)
\(\Rightarrow1+\frac{2}{2017^{10}-1}< 1+\frac{2}{2017^{10}-1}\)
\(\Rightarrow\frac{2017^{10}+1}{2017^{10}-1}< \frac{2017^{10}-1}{2017^{10}-3}\)
Vì \(A=\dfrac{10^{2017}-2}{10^{2017}+1}< 1\)
\(\Rightarrow B=\dfrac{10^{2017}-2}{10^{2017}+1}< \dfrac{10^{2017}-2+2}{10^{2017}+1+2}=\dfrac{10^{2017}}{10^{2017}+3}=A\)
Vậy A > B
Vì \(A< 1\)
\(\Rightarrow A< \dfrac{10^{2017}-2+2}{10^{2017}+1+2}=\dfrac{10^{2017}}{10^{2017}+3}=B\)
Vậy A < B