a: =-8/28-7/28=-15/28

b: \(=\dfrac{-4}{18}+\dfrac{3}{7}\cdot\dfrac{14}{15}=\dfrac{-2}{9}+\dfrac{14}{15}=\dfrac{-10+42}{45}=\dfrac{32}{45}\)

c: \(=\dfrac{-3\cdot5+7\cdot2}{20}\cdot\dfrac{-5}{1}-\dfrac{2}{9}\)

\(=\dfrac{-7}{4}-\dfrac{2}{9}=\dfrac{-63}{36}-\dfrac{8}{36}=-\dfrac{71}{36}\)

\(a,\dfrac{-2}{7}-\dfrac{1}{4}\)

\(=\dfrac{-8}{28}-\dfrac{7}{28}\)

\(=\dfrac{-15}{28}\)

\(b,\dfrac{-1}{2}.\dfrac{4}{9}+\dfrac{3}{7}\div\dfrac{15}{14}\)

-29/36

\(0,2\times\dfrac{15}{36}-\left(\dfrac{2}{5}+\dfrac{2}{3}\right):1\dfrac{1}{5}\)

=\(\dfrac{1}{5}\times\dfrac{15}{36}-\dfrac{16}{15}:\dfrac{6}{5}\)

=\(\dfrac{1}{12}-\dfrac{8}{9}\)

= \(-\dfrac{29}{36}\)

Tìm x:

a) \(\left(-1\dfrac{1}{5}+x\right):\left(-3\dfrac{3}{5}\right)=-\dfrac{7}{4}+\dfrac{1}{4}:\dfrac{1}{8}\)

\(\left(-1\dfrac{1}{5}+x\right):\left(-3\dfrac{3}{5}\right)=\dfrac{1}{4}\)

\(-1\dfrac{1}{5}+x=\dfrac{1}{4}.\left(-3\dfrac{3}{5}\right)\)

\(-1\dfrac{1}{5}+x=\dfrac{-9}{10}\)

\(\Rightarrow x=\dfrac{3}{10}\)

b) \(\dfrac{5}{7}+\dfrac{2}{3}x=\dfrac{3}{10}\)

\(\dfrac{2}{3}x=\dfrac{3}{10}-\dfrac{5}{7}\)

\(\dfrac{2}{3}x=\dfrac{-29}{70}\)

\(\Rightarrow x=\dfrac{-87}{140}\)

c) \(\dfrac{-22}{15}x+\dfrac{1}{3}=\left|\dfrac{-2}{3}+\dfrac{1}{5}\right|\)

\(-\dfrac{22}{15}x+\dfrac{1}{3}=\dfrac{7}{15}\)

\(\dfrac{-22}{15}x=\dfrac{4}{15}-\dfrac{1}{3}\)

\(\dfrac{-22}{15}x=\dfrac{2}{15}\)

\(\Rightarrow x=\dfrac{-1}{11}\)

\(\left[\dfrac{6}{5}-\left(\dfrac{3}{7}-2\dfrac{1}{7}\right):\dfrac{4}{7}\right]\left(-\dfrac{3}{5}\right)+\dfrac{2}{3}:\left(-\dfrac{5}{6}\right)\\ =\left[\dfrac{6}{5}-\left(\dfrac{3}{7}-\dfrac{15}{7}\right)\cdot\dfrac{7}{4}\right]\left(-\dfrac{3}{5}\right)+\dfrac{2}{3}\cdot\left(-\dfrac{6}{5}\right)\\ =\left[\dfrac{6}{5}+3\right]\left(-\dfrac{3}{5}\right)-\dfrac{4}{5}\\ =\dfrac{21}{5}\cdot\left(-\dfrac{7}{5}\right)\\ =-\dfrac{147}{25}\)

câu a thì 15 nhân voi 3/5 hay là \(15\dfrac{3}{5}\) là một hỗn số

`a)((sqrt(14)-sqrt7)/(1-sqrt2)+(sqrt{15}-sqrt5)/(1-sqrt3)):1/(sqrt7-sqrt5)`

`=((sqrt7(sqrt2-1))/(1-sqrt2)+(sqrt5(sqrt3-1))/(1-sqrt3)).(sqrt7-sqrt5)`

`=(-sqrt7-sqrt5)*(sqrt7-sqrt5)`

`=-(sqrt7+sqrt5)(sqrt7+sqrt5)`

`=-(7-5)=-2`

`b)sqrt2+1/sqrt{5+2sqrt6}+2/sqrt{8+2sqrt{15}}`

`=sqrt2+1/sqrt{3+2sqrt{3}.sqrt2+2}+2/sqrt{5+2sqrt{5}.sqrt3+3}`

`=sqrt2+1/sqrt{(sqrt3+sqrt2)^2}+2/sqrt{(sqrt5+sqrt3)^2}`

`=sqrt2+1/(sqrt3+sqrt2)+2/(sqrt5+sqrt3)`

`=sqrt2+((sqrt3+sqrt2)(sqrt3-sqrt2))/(sqrt3+sqrt2)+((sqrt5+sqrt3)(sqrt5-sqrt3))/(sqrt5+sqrt3)`

`=sqrt2+sqrt3-sqrt2+sqrt5-sqrt3=sqrt5`

a) Ta có: \(\left(\dfrac{\sqrt{14}-\sqrt{7}}{1-\sqrt{2}}+\dfrac{\sqrt{15}-\sqrt{5}}{1-\sqrt{3}}\right):\dfrac{1}{\sqrt{7}-\sqrt{5}}\)

\(=\left(-\dfrac{\sqrt{7}\left(1-\sqrt{2}\right)}{1-\sqrt{2}}-\dfrac{\sqrt{5}\left(1-\sqrt{3}\right)}{1-\sqrt{3}}\right):\dfrac{1}{\sqrt{7}-\sqrt{5}}\)

\(=-2\)

b) Ta có: \(\sqrt{2}+\dfrac{1}{\sqrt{5+2\sqrt{6}}}+\dfrac{2}{\sqrt{8+2\sqrt{15}}}\)

\(=\sqrt{2}+\dfrac{1}{\sqrt{3}+\sqrt{2}}+\dfrac{2}{\sqrt{5}+\sqrt{3}}\)

\(=\sqrt{2}+\sqrt{3}-\sqrt{2}+\sqrt{5}-\sqrt{3}\)

\(=\sqrt{5}\)

a: =>x*2/15=2/7

=>x=2/7:2/15=2/7*15/2=15/7

b: x=3:7/5=15/7

c: x=-1/2:4/9=-1/2*9/4=-9/8

d: x=-8/3:3/8=-64/9

g: =>4/11x=2/5+1/3=6/15+5/15=11/15

=>x=11/15:4/11=121/60

l: =>1/4:x=1-3/2=-1/2

=>x=-1/4:1/2=-1/4*2=-1/2

k: =>x:7=-1/3+5/2=-2/6+15/6=13/6

=>x=91/6

b) \(\dfrac{7}{15}-\dfrac{9}{19}\)\(-\dfrac{-8}{15}-\dfrac{10}{19}\)
=\(\left(\dfrac{7}{15}-\dfrac{8}{15}\right)\) \(-\left(\dfrac{9}{19}-\dfrac{10}{19}\right)\)
= \(-\dfrac{1}{15}\) - \(\left(-\dfrac{1}{19}\right)\)
\(=-\dfrac{1}{15}\) + \(\dfrac{1}{19}\)

= \(-\dfrac{4}{285}\)

c) \(1\dfrac{1}{3}\) \(\div\) \(\dfrac{4}{5}\) + 2\(\dfrac{2}{3}\) \(\div\)\(\dfrac{4}{5}\)
= \(\left(1\dfrac{1}{3}+2\dfrac{2}{3}\right)\) \(\div\dfrac{4}{5}\)
= \(\left[\left(1+2\right)+\left(\dfrac{1}{3}+\dfrac{2}{3}\right)\right]\) \(\div\dfrac{4}{5}\)
= ( 3 + 1 ) \(\div\dfrac{4}{5}\)
= 4 \(\div\dfrac{4}{5}\)
= \(\dfrac{4.5}{4}\)
= 5

\(\dfrac{15}{16}:\dfrac{5}{8}\times\dfrac{3}{4}\)

\(=\dfrac{15}{16}\times\dfrac{8}{5}\times\dfrac{3}{4}\)

\(=\dfrac{3}{2}\times\dfrac{3}{4}\)

\(=\dfrac{9}{8}\)

_________________

\(\dfrac{21}{4}\times\dfrac{16}{14}\times\dfrac{1}{2}\times\dfrac{8}{3}\)

\(=6\times\dfrac{4}{3}\)

\(=8\)

e) \(\dfrac{-3}{5}.\dfrac{2}{7}+\dfrac{-3}{5}.\dfrac{5}{7}+2\dfrac{3}{5}\)

= \(\dfrac{-3}{5}.\left(\dfrac{2}{7}+\dfrac{5}{7}\right)+\dfrac{13}{5}\)

= \(\dfrac{-3}{5}.1+\dfrac{13}{5}\)

= \(\dfrac{-3}{5}+\dfrac{13}{5}\)

= 2