\(B=3.\left(\frac{1}{1.4}+\frac{1}{4.7}+\frac{1}{7.10}+........+\frac{1}{27.30}\right)\)
\(B=3.\frac{1}{3}.\left(\frac{1}{1}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-.......-\frac{1}{27}+\frac{1}{27}-\frac{1}{30}\right)\)
\(B=1.\left(\frac{1}{1}-\frac{1}{30}\right)\)
\(B=\frac{29}{30}\)
B =\(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{27.30}\)
B = \(\frac{1}{1}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{27}-\frac{1}{30}\)
B =\(\frac{1}{1}-\frac{1}{30}\)
B =\(\frac{29}{30}\)
Ta có:
\(B=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{27.30}\)
\(=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{27}-\frac{1}{30}\)
\(=1-\frac{1}{30}=\frac{29}{30}\)
Vậy \(B=\frac{29}{30}\)
\(B=\frac{3}{1\cdot4}+\frac{3}{4\cdot7}+\frac{3}{7\cdot10}+...+\frac{3}{27\cdot30}\)
\(B=\frac{1}{1}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{27}-\frac{1}{30}\)
\(B=\frac{1}{1}-\left(\frac{1}{4}-\frac{1}{4}\right)-\left(\frac{1}{7}-\frac{1}{7}\right)-...-\left(\frac{1}{27}-\frac{1}{27}\right)-\frac{1}{30}\)
\(B=\frac{1}{1}-\frac{1}{30}\)
\(B=\frac{29}{30}\)
Ta có : B =\(\frac{1}{1}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+.......+\frac{1}{27}-\frac{1}{30}\)\(\frac{1}{30}\)
=>B = \(\frac{1}{1}-\frac{1}{30}\)
=>B = \(\frac{29}{30}\)
\(B=\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{27.30}\)
\(B=\frac{3}{3}\left(\frac{4}{1.4}+\frac{4}{4.7}+\frac{4}{7.10}+...+\frac{4}{27.30}\right)\)
\(B=\frac{3}{3}\left(\frac{4-1}{1.4}+\frac{7-4}{4.7}+\frac{10-7}{7.10}+...+\frac{30-27}{27.30}\right)\)
\(B=\frac{3}{3}\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{27}-\frac{1}{30}\right)\)
\(B=\frac{3}{3}.\left(1-\frac{1}{30}\right)\)
\(B=\frac{3}{3}.\frac{29}{30}\)
\(B=\frac{29}{30}\)
P/S: Mình mới lớp 5 không biết có làm đúng không :))
B=\(\frac{1}{1}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{27}-\frac{1}{30}\)
B=\(\frac{1}{1}-\frac{1}{30}\)
B= \(\frac{29}{30}\)