\(\dfrac{5}{3}=5:3\)

Vậy \(2\) số đó là \(5\) và \(3\)

\(\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{19.20}\)

\(=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+...+\dfrac{1}{19}-\dfrac{1}{20}\)

\(=\dfrac{1}{2}-\dfrac{1}{20}\)

\(=\dfrac{9}{20}\)

\(A=\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{19.20}\)

\(A=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+...+\dfrac{1}{19}-\dfrac{1}{20}\)

\(A=\dfrac{1}{2}-\dfrac{1}{20}=\dfrac{10}{20}-\dfrac{1}{20}=\dfrac{9}{20}\)

1, \(\sqrt{x^2+1}=2\Leftrightarrow x^2+1=4\Leftrightarrow x=\pm\sqrt{3}\)

2, \(\dfrac{19}{2}-\dfrac{3}{4}\left|x-\dfrac{1}{3}\right|=\dfrac{19}{3}-\dfrac{1}{3}\left|x-\dfrac{1}{3}\right|\)

\(\Leftrightarrow\dfrac{19}{6}+\dfrac{7}{12}\left|x-\dfrac{1}{3}\right|=0\Leftrightarrow\dfrac{7}{12}\left|x-\dfrac{1}{3}\right|=-\dfrac{19}{6}\left(voli\right)\)

dell biết

\(12+x< 9-x\Leftrightarrow x+x< 9-12\Leftrightarrow2x< -3\Leftrightarrow x< -\dfrac{3}{2}\)

(50 - 6x) .18 = 23.32.5

50.18 - 6.18.x = 3680

900 - 108x = 3680

108x = 900 - 3680

108x =- 2780

x = -2780: 108

x = -695/27