\(\frac{9\cdot8\cdot33}{56\cdot54\cdot11}=\frac{9\cdot8\cdot3\cdot11}{8\cdot7\cdot9\cdot3\cdot2\cdot11}=\frac{1}{7\cdot2}=\frac{1}{14}\)

\(\frac{8\cdot15+16\cdot4-8\cdot21}{16\cdot5-8\cdot9}=\frac{8\cdot15+8\cdot2\cdot4-8\cdot21}{2\cdot8\cdot5-8\cdot9}=\frac{8\cdot15+8\cdot8-8\cdot21}{8\cdot10-8\cdot9}=\frac{8\left(15+8-21\right)}{8\left(10-9\right)}=\frac{8\cdot2}{8\cdot1}=\frac{2}{1}=2\)

=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6

=1/2-1/6=1/3

\(\dfrac{1}{2\times3}+\dfrac{1}{3\times4}+\dfrac{1}{4\times5}+\dfrac{1}{5\times6}=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}=\dfrac{1}{2}-\dfrac{1}{6}=\dfrac{3-1}{6}=\dfrac{2}{6}=\dfrac{1}{3}\)

=1/2-1/3+1/3-1/4+...+1/6-1/7

=1/2-1/7

=5/14

??????????????

\(=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}\)

\(=\dfrac{1}{2}-\dfrac{1}{6}\)

\(=\dfrac{1}{3}\)

\(=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}=\dfrac{1}{2}-\dfrac{1}{6}=\dfrac{1}{3}\)

giúp mik với mik cần gấp lắm

mik sẽ tích co bn trả lời đầu tiên(nếu đúng nha)

a: Ta có: \(A=\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}\)

\(=\frac12-\frac13+\frac13-\frac14+\frac14-\frac15+\frac15-\frac16\)

\(=\frac12-\frac16=\frac36-\frac16=\frac26=\frac13\)

b: Ta có: \(B=\frac{3}{7\cdot10}+\frac{24}{10\cdot14}-\frac{35}{14\cdot21}+\frac{49}{21\cdot70}\)

\(=\frac17-\frac{1}{10}+\frac{1}{10}+\frac{1}{14}-\frac{1}{14}-\frac{1}{21}+\frac{1}{21}-\frac{1}{70}\)

\(=\frac17-\frac{1}{70}=\frac{9}{70}\)

Trả lời :

\(\frac{1}{2\times3}+\frac{1}{3\times4}+\frac{1}{4\times5}=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}=\frac{1}{2}-\frac{1}{5}=\frac{3}{10}\)

~Std well~

#Dương