Question

Chứng tỏ :

1/20+1/21+1/22+...+1/27>8/27

Answer 1

ta có \(\frac{1}{20}>\frac{1}{27};\frac{1}{21}>\frac{1}{27}...;\frac{1}{26}>\frac{1}{27}\)

=> \(\frac{1}{20}+\frac{1}{21}+...+\frac{1}{27}>\frac{7}{27}+\frac{1}{27}=\frac{8}{27}\)(ĐPcm)

Answer 2

Ta có : \(\frac{1}{20}+\frac{1}{21}+\frac{1}{22}+...+\frac{1}{27}\)(8 số hạng)

\(>\frac{1}{27}+\frac{1}{27}+\frac{1}{27}+...+\frac{1}{27}\)(8 số hạng)

\(=\frac{1}{27}\times8\)

\(=\frac{8}{27}\)

\(\Rightarrow\frac{1}{20}+\frac{1}{21}+\frac{1}{22}+...+\frac{1}{27}>\frac{8}{27}\left(đpcm\right)\)

Answer 3

Vì \(\frac{1}{20}< \frac{1}{27};\frac{1}{21}< \frac{1}{27};...;\frac{1}{26}< \frac{1}{27}\)

\(\frac{\Rightarrow1}{20}+\frac{1}{21}+...+\frac{1}{27}>\frac{7}{27}+\frac{1}{27}=\frac{8}{27}\left(ĐPCM\right)\)

Answer 4

Đpcm là gì

Answer 5

                                                       Bài giải

Ta có : \(\frac{1}{20}+\frac{1}{21}+\frac{1}{22}+...+\frac{1}{27}>\frac{1}{27}+\frac{1}{27}+\frac{1}{27}+...+\frac{1}{27}=\frac{8}{27}\)

\(\Rightarrow\text{ ĐPCM}\)

Answer 6

                                                       Bài giải

Ta có : \(\frac{1}{20}+\frac{1}{21}+\frac{1}{22}+...+\frac{1}{27}>\frac{1}{27}+\frac{1}{27}+\frac{1}{27}+...+\frac{1}{27}=\frac{8}{27}\)

\(\Rightarrow\text{ ĐPCM}\)

Answer 7

Giải

Ta có : \(\frac{1}{20}+\frac{1}{21}+\frac{1}{22}+...+\frac{1}{27}>\frac{1}{27}+\frac{1}{27}+\frac{1}{27}+...+\frac{1}{27}=\frac{8}{27}\)

\(\Rightarrowđpcm\)

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