Toán

S

supperman091

Last edited by a moderator:
P

pro3182001

A=$\frac{1}{41}$+$\frac{1}{42}$+$\frac{1}{43}$+...+$\frac{1}{80}$
=($\frac{1}{41}$+$\frac{1}{42}$+...+$\frac{1}{60}$)+($\frac{1}{61}$+$\frac{1}{62}$+...+$\frac{1}{80}$)
\Rightarrow A>$\frac{1}{60}$.20+$\frac{1}{80}$.20
\Rightarrow A>$\frac{1}{3}$+$\frac{1}{4}$
\Rightarrow A>$\frac{7}{12}$
 
You must log in or register to reply here.
Top Bottom