Question

Chứng minh:

S= 5/20 + 5/21 + 5/22 + 5/23 + 5/24 > 1

Answer 1

Ta có :

\(\frac{5}{20}>\frac{5}{25}\)

\(\frac{5}{21}>\frac{5}{25}\)

\(\frac{5}{22}>\frac{5}{25}\)

\(\frac{5}{23}>\frac{5}{25}\)

\(\frac{5}{24}>\frac{5}{25}\)

\(\Rightarrow\frac{5}{20}+\frac{5}{21}+\frac{5}{22}+\frac{5}{23}+\frac{5}{24}>5.\frac{5}{25}=1\)

\(\Rightarrow\frac{5}{20}+\frac{5}{21}+\frac{5}{22}+\frac{5}{23}+\frac{5}{24}>1\)

Answer 2

ta có S=5/20+5/21+5/22+5/23+5/24>5/25+5/25+5/25+5/25+5/25=5/25*5=1

=>đpcm