C = 3/4.7 + 3/7.10 + 3/10.13 + ... + 3/73.76
=1/4 - 1/7 + 1/7 - 1/10 + 1/10 - 1/13 + ... + 1/73 - 1/76
=1/4 - 1/76
=18/76
\(C=\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+......+\frac{1}{73}-\frac{1}{76}\)
\(=\frac{1}{4}-\frac{1}{76}\)
\(=\frac{19}{76}-\frac{1}{76}\)
\(=\frac{18}{76}=\frac{9}{38}\)
\(C=\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+...+\frac{3}{73.76}\)
\(C=\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{73}-\frac{1}{76}\)
\(C=\frac{1}{4}-\frac{1}{76}\)
\(C=\frac{9}{38}\)
Ta có :
\(C=\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{73.76}\)
\(C=\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{73}-\frac{1}{76}\)
\(C=\frac{1}{4}-\frac{1}{76}=\frac{18}{76}=\frac{9}{38}\)
Ủng hộ mk nha ^_^
C=\(\frac{3}{4.7}\)+\(\frac{3}{7.10}\)+\(\frac{3}{10.13}\)+.........+\(\frac{3}{73.76}\)
C=\(\frac{3}{4}\)-3
\(C=\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+...+\frac{3}{73.76}\)
\(C=\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{73}-\frac{1}{76}\)
\(C=\frac{1}{4}-\frac{1}{76}\)
\(C=\frac{9}{38}\)