1:

a: \(=\dfrac{-4}{7}+\dfrac{4}{7}+\dfrac{3}{7}-\dfrac{23}{34}-\dfrac{4}{5}=\dfrac{3}{7}-\dfrac{23}{34}-\dfrac{4}{5}=-\dfrac{1247}{1190}\)

b:

Sửa đề: \(\dfrac{-5}{13}+\dfrac{4}{19}+\dfrac{-8}{13}+\dfrac{15}{19}+\dfrac{45}{6}\) 

\(=\dfrac{-5}{13}-\dfrac{8}{13}+\dfrac{4}{19}+\dfrac{15}{19}+\dfrac{45}{6}=\dfrac{9}{2}\)

\(3^6\cdot45^4-15^{13}\cdot5^{-9}\)

\(=3^6\cdot\left(3^2\cdot5\right)^4-\left(3\cdot5\right)^{13}\cdot5^{-9}\)

\(=3^6\cdot3^8\cdot5^4-3^{13}\cdot5^{13}\cdot5^{-9}=3^{14}\cdot5^4-3^{13}\cdot5^4=3^{13}\cdot5^4\left(3-1\right)=3^{13}\cdot5^4\cdot2\)

\(27^4\cdot25^3+45^6\)

\(=\left(3^3\right)^4\cdot\left(5^2\right)^3+\left(3^2\cdot5\right)^6\)

\(=3^{12}\cdot5^6+3^{12}\cdot5^6=2\cdot3^{12}\cdot5^6\)

Ta có: \(\frac{3^6\cdot45^4-15^{13}\cdot5^{-9}}{27^4\cdot25^3+45^6}\)

\(=\frac{3^{13}\cdot5^4\cdot2}{2\cdot3^{12}\cdot5^6}\)

\(=\frac{3}{5^2}=\frac{3}{25}\)

\(\frac{2}{3}\times\frac{3}{4}\times\frac{4}{5}:\frac{1}{5}\)

\(=\frac{2\times3\times4}{3\times4\times5}:\frac{1}{5}\)

\(=\frac{2}{5}:\frac{1}{5}\)

\(=\frac{2}{5}\times5\)

\(=2\)

                                                            Bài giải

\(\frac{2}{3}+\frac{3}{4}+\frac{4}{5}=\frac{40}{60}+\frac{45}{60}+\frac{48}{60}=\frac{133}{60}\)

\(\frac{8}{5}+\frac{7}{6}+\frac{10}{9}+\frac{1}{2}=\frac{144}{90}+\frac{105}{90}+\frac{100}{90}+\frac{45}{90}=\frac{394}{90}\)

\(\frac{15}{17}-\frac{11}{13}+\frac{3}{26}=\frac{390}{442}+\frac{374}{442}+\frac{51}{442}=\frac{815}{442}\)

\(\frac{9}{12}\text{ x }\frac{4}{3}\text{ : }\frac{8}{5}=\frac{9}{12}\text{ x }\frac{4}{3}\text{ x }\frac{5}{8}=\frac{9\text{ x }4\text{ x }5}{12\text{ x }3\text{ x }8}=\frac{5}{8}\)

\(\frac{4}{5}\text{ x }\frac{15}{8}\text{ : }\frac{5}{7}=\frac{4}{5}\text{ x }\frac{15}{8}\text{ x }\frac{7}{5}=\frac{4\text{ x }15\text{ x }7}{5\text{ x }8\text{ x }5}=\frac{21}{10}\)

\(\frac{2}{3}+\frac{3}{4}+\frac{4}{5}=\frac{40}{60}+\frac{45}{60}+\frac{48}{60}=\frac{133}{60}\) 

\(\frac{8}{5}+\frac{7}{6}+\frac{10}{9}+\frac{1}{2}=\frac{144}{90}+\frac{105}{90}+\frac{100}{90}+\frac{45}{90}=\frac{197}{45}\)

\(\frac{15}{17}-\frac{11}{13}+\frac{1}{26}=\frac{390}{442}+\frac{374}{442}+\frac{51}{442}=\frac{815}{442}\)

\(\frac{9}{12}\times\frac{4}{3}:\frac{8}{5}=1:\frac{8}{5}=\frac{5}{8}\)

\(\frac{4}{5}\times\frac{15}{8}:\frac{5}{7}=\frac{3}{2}:\frac{5}{7}=\frac{21}{10}\)

khó cậu ạ

a)\(x-15\%x=\frac{1}{3}\)

\(x.\left(1-15\%\right)=\frac{1}{3}\)

\(x.\frac{-280}{3}=\frac{1}{3}\)

\(x=\frac{1}{3}:\frac{-280}{3}\)

\(x=\frac{-1}{280}\)

Vậy \(x=\frac{-1}{280}\)

b)\(\frac{4}{5}x-x-\frac{3}{2}x+\frac{6}{5}=\frac{1}{2}-\frac{4}{3}\)

\(-\frac{17}{10}x+\frac{6}{5}=\frac{-5}{6}\)

\(-\frac{17}{10}x=-\frac{5}{6}-\frac{6}{5}\)

\(-\frac{17}{10}x=\frac{-61}{30}\)

\(x=\frac{-61}{30}:\frac{-17}{10}\)

\(x=\frac{61}{51}\)

Vậy \(x=\frac{61}{51}\)