S = 1 - 1/4 + 1/4 - 1/7 + 1/7 - 1/10 +.............+ 1/40 - 1/43 + 1/43 - 1/46
S = 1 - 1/46
S = 45/46 < 1
=> S < 1 (đpcm)
*** k mk nha các bạn ***
\(s=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{43.46}\)
\(\Rightarrow s=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+.....+\frac{1}{43}-\frac{1}{46}\)
\(\Rightarrow S=1-\frac{1}{46}=\frac{45}{46}\)
Tao có \(\frac{45}{46}<1\) => S < 1