Question

S= 1/21+1/22+1/23+1/24+.........+1/150. So sanh S với 5/4

GIÚP MIK VỚI

Answer 1

\(S=\frac{1}{21}+\frac{1}{22}+...+\frac{1}{150}\)

\(=\left(\frac{1}{21}+...+\frac{1}{40}\right)+\left(\frac{1}{41}+...+\frac{1}{80}\right)+\left(\frac{1}{81}+...+\frac{1}{150}\right)\)

\(>\left(\frac{1}{40}+...+\frac{1}{40}\right)+\left(\frac{1}{80}+...+\frac{1}{80}\right)+\left(\frac{1}{150}+...+\frac{1}{150}\right)\)

\(=\frac{20}{40}+\frac{40}{80}+\frac{70}{150}\)

\(=\frac{1}{2}+\frac{1}{2}+\frac{7}{15}>\frac{5}{4}\)