`9/14 : 3/7 + 5/6 = 3/98 + 5/6 = 127/147`

__________________

`4/7 xx (4 - 7/3) = 4/7 xx 5/3 = 20/21`

\(\dfrac{9}{14}:\dfrac{3}{7}+\dfrac{5}{6}=\dfrac{9}{14}\times\dfrac{7}{3}+\dfrac{5}{6}=\dfrac{3}{2}+\dfrac{5}{6}=\dfrac{7}{3}\)

\(\dfrac{4}{7}\times\left(4-\dfrac{7}{3}\right)=\dfrac{4}{7}\times\dfrac{5}{3}=\dfrac{20}{21}\)

\(A< \dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+...+\dfrac{1}{2003.2004}\)

\(\Rightarrow A< \dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+...+\dfrac{1}{2003}-\dfrac{1}{2004}\)

\(\Rightarrow A< \dfrac{1}{4}-\dfrac{1}{2004}< \dfrac{1}{4}\)

Đồng thời:

\(A>\dfrac{1}{5.6}+\dfrac{1}{6.7}+\dfrac{1}{7.8}+...+\dfrac{1}{2004.2005}\)

\(A>\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+...+\dfrac{1}{2004}-\dfrac{1}{2005}\)

\(A>\dfrac{1}{5}-\dfrac{1}{2005}=\dfrac{80}{401}>\dfrac{50}{500}>\dfrac{1}{10}>\dfrac{1}{65}\)

Vậy \(\dfrac{1}{65}< A< \dfrac{1}{4}\)

3/4 x 4/5 x 5/3 x 8/3 = 8/3

\(\dfrac{3}{4}:\dfrac{5}{4}:\dfrac{3}{5}:\dfrac{3}{8}=\dfrac{3}{5}:\dfrac{3}{5}:\dfrac{3}{8}=1:\dfrac{3}{8}=\dfrac{8}{3}\)

5/2 - 1/4 + 5/3

= 10/4 - 1/4 + 5/3

= 9/4 + 5/3

= 27/12 + 20/12

= 47/12

11/2 : 1/4 x 5/3

= 11/2 x 4/1 x 5/3

= 44/2 x 5/3

= 220/6

= 110/3

14/5 x 2/3 + 5

= 28/15 + 5

= 28/15 + 75/15

= 103/15

nhớ ghi cách giải nha mình tick luôn

a: =11/2*4*5/3

=22*5/3

=110/3

b: =30/12-3/12+20/12

=47/12

c: =28/15+5

=28/15+75/15

=103/15

\(5,\dfrac{4}{x-2}+\dfrac{x}{x+1}-\dfrac{x^2-2}{\left(x-2\right)\left(x+1\right)}=0\left(dkxd:x\ne2;-1\right)\)

\(\Rightarrow4\left(x+1\right)+x\left(x-2\right)-x^2-2=0\)

\(\Rightarrow4x+4+x^2-2x-x^2-2=0\)

\(\Rightarrow2x+2=0\)

\(\Rightarrow x=-1\left(loai\right)\)

Vậy \(S=\varnothing\)

em c.ơn nhiều ạ 

a: =>1/3(2x-5)=-2/3-3/2=-4/6-9/6=-13/6

=>2x-5=-13/6*3=-13/2

=>2x=-3/2

=>x=-3/4

b: =>2/5x=-3/4-1/2=-5/4

=>x=-5/4:2/5=-5/4*5/2=-25/8

a)

 \(-\dfrac{2}{3}-\dfrac{1}{3}\left(2x-5\right)=\dfrac{3}{2}\\ \Rightarrow\dfrac{1}{3}\left(2x-5\right)=-\dfrac{2}{3}-\dfrac{3}{2}\\ \Rightarrow\dfrac{1}{3}\left(2x-5\right)=-\dfrac{13}{6}\\ \Rightarrow2x-5=-\dfrac{13}{6}:\dfrac{1}{3}=-\dfrac{13}{2}\\ \Rightarrow2x=-\dfrac{13}{2}+5\\ \Rightarrow2x=-\dfrac{3}{2}\\ \Rightarrow x=-\dfrac{3}{2}:2\\ \Rightarrow x=-\dfrac{3}{4}\)

b)

\(\dfrac{2}{5}x+\dfrac{1}{2}=-\dfrac{3}{4}\\ \Rightarrow\dfrac{2}{5}x=-\dfrac{3}{4}-\dfrac{1}{2}\\ \Rightarrow\dfrac{2}{5}x=-\dfrac{5}{4}\\ \Rightarrow x=-\dfrac{5}{4}:\dfrac{2}{5}=-\dfrac{25}{8}\)

a)

= nhau nha

\(2/3*4/5=8/15\)

\(4/5*2/3=8/15\)

\(=>2/3*4/5=4/5*2/3\) nhé