Ta thấy: \(\frac{1}{3}\)- \(\frac{1}{30}\)- \(\frac{1}{5}\)- \(\frac{1}{10}\)
= \(\frac{10}{30}\)- \(\frac{1}{30}\)- \(\frac{6}{30}\)- \(\frac{3}{30}\)= 0
nên gtbt trên bằng 0
\(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}x\frac{x}{3}=\frac{5}{21}\)
Chứng minh : \(\frac{1}{1}-\frac{1}{1}+\frac{1}{2}-\frac{1}{3}+\frac{1}{5}-\frac{1}{8}+\frac{1}{13}-\frac{1}{21}+\frac{1}{34}-\frac{1}{55}+...< \frac{3}{10}\).
Tính nhanh:
P = \(\frac{1}{5x8}+\frac{1}{8x11}+\frac{1}{11x14}+..........+\frac{1}{602x605}\)
Q = \(\frac{4}{3x7}+\frac{5}{7x12}+\frac{1}{12x13}+\frac{7}{13x20}+\frac{3}{20x23}\)
R = \(\left(1-\frac{1}{15}\right)\times\left(1-\frac{1}{21}\right)\times\left(1-\frac{1}{28}\right)\times........\times\left(1-\frac{1}{210}\right)\)
\(\frac{14}{16}\) - \(\frac{6}{21}\)
\(\frac{9}{22}\) - \(\frac{9}{33}\)
\(\frac{8}{15}\)+ \(\frac{4}{21}\)
\(\frac{15}{24}+2\)
\(\frac{4}{5}-\frac{1}{3}+\frac{1}{2}\)
\(\frac{5}{6}+\frac{3}{8}+\frac{1}{10}\)
\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}\)
Tính nhanh:
a)\(\frac{5}{30}+\frac{15}{90}+\frac{25}{150}+\frac{35}{210}+\frac{45}{270}\)
b)\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{56}\)
c)\(\frac{1}{15}+\frac{4}{30}+\frac{2}{45}+\frac{16}{60}+\frac{25}{75}+\frac{36}{90}+\frac{49}{105}+\frac{64}{120}+\frac{81}{135}\)
1+\(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+...\frac{1}{300}\)
\(\frac{x}{2008}-\frac{1}{10}-\frac{1}{15}-\frac{1}{21}-...-\frac{1}{120}=\frac{5}{8}\)
\(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+\frac{1}{28}\)
Tính nhanh
\(\frac{2014+\frac{2013}{2}+\frac{2012}{3}+\frac{2011}{4}+\frac{2010}{5}+...+\frac{2}{2013}+\frac{1}{2014}}{\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+\frac{1}{5}+...+\frac{1}{2012}+\frac{1}{2013}+\frac{1}{2014}}\)
Giải tự luận hộ mình nha!!!!!!!! Mình cảm ơn!!!
