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![](https://rs.olm.vn/images/avt/0.png?1311)
305 x 207 + 305
305 x 207 + 305 x 1
305 x (207 + 1 )
305 x 208
=63440
còn câu a mik ko bít
so sánh
dam ha2 ... 77 dam2
15 ha 304 m2 ... 150 304 m2
75 ha 3 dam2... 3/4 km2
9 ha 99 m2 ... 1/10 km2
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
a, \(A=\frac{1}{2\cdot2}+\frac{1}{3\cdot3}+\frac{1}{4\cdot4}+...+\frac{1}{2011\cdot2011}\)
có :
\(\frac{1}{2\cdot2}< \frac{1}{1\cdot2}\)
\(\frac{1}{3\cdot3}< \frac{1}{2\cdot3}\)
\(\frac{1}{4\cdot4}< \frac{1}{3\cdot4}\)
...
\(\frac{1}{2011\cdot2011}< \frac{1}{2010\cdot2011}\)
nên :
\(A< \frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{2010\cdot2011}\)
\(\Rightarrow A< 1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2010}-\frac{1}{2011}\)
\(\Rightarrow A< 1-\frac{1}{2011}\)
\(\Rightarrow A< \frac{2010}{2011}< 1\)
b, \(A=\frac{2010}{2011}=1-\frac{1}{2011}\)
\(\frac{3}{4}=1-\frac{1}{4}\)
\(\frac{1}{4}>\frac{1}{2011}\)
nên :
\(A>\frac{3}{4}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(Giải\)
\(\Rightarrow A=\frac{1}{2}-\frac{1}{2}+\frac{1}{3}-\frac{1}{3}\)\(+\frac{1}{4}-\frac{1}{4}+...+\frac{1}{2014}-\frac{1}{2014}\)
\(A=0+0+0+...+0+0\)
\(\Rightarrow A=0\)
\(a.\)\(A< 1\)
b. \(A< \frac{3}{4}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
122 =14
132 <12.3
.............
11002 <199.100
⇒A<14 +12.3 +....+199.100
⇒A<14 +12 −13 +...+199 −1100
⇒A<14 +12 −1100
⇒A<14 <34
\(A=\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{100^2}\)
\(A>\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+...+\frac{1}{100\cdot101}\)
\(A>\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{100}-\frac{1}{101}\)
\(A>\frac{1}{2}-\frac{1}{101}=\frac{99}{202}>\frac{2}{3}\)
\(\Rightarrow A>\frac{2}{3}\)
nhỏ hơn 1 nha
\(\frac{2012\times2014+305}{2011\times2014+304}\)
\(\text{Ta so sánh : 2012 x 2014 + 305 và 2011 x 2014 + 304}\)
\(\text{Vì }2012\times2014>2011\times2014\)
\(\text{Mà 305 }>304\)
\(\Rightarrow2012\times2014+305>2011\times2014+304\)
\(\Rightarrow\frac{2012\times2014+305}{2011\times2014+304}>1\)