`!`

\(a,\dfrac{8}{9}\times\dfrac{7}{5}-\dfrac{7}{9}\times\dfrac{2}{5}+\dfrac{2}{9}\\ =\dfrac{8}{9}\times\left(\dfrac{7}{5}-\dfrac{2}{5}\right)+\dfrac{2}{9}\\ =\dfrac{8}{9}\times\dfrac{5}{5}+\dfrac{2}{9}\\ =\dfrac{8}{9}+\dfrac{2}{9}\\ =\dfrac{10}{9}\)

\(b,\dfrac{5}{9}\times\dfrac{1}{4}+\dfrac{4}{9}\times\dfrac{3}{12}\\ =\dfrac{5}{9}\times\dfrac{1}{4}+\dfrac{4}{9}\times\dfrac{1}{4}\\ =\dfrac{1}{4}\times\left(\dfrac{5}{9}+\dfrac{4}{9}\right)\\ =\dfrac{1}{4}\times\dfrac{9}{9}\\ =\dfrac{1}{4}\)

   \(\dfrac{8}{9}\) \(\times\) \(\dfrac{7}{5}\) - \(\dfrac{7}{9}\) \(\times\) \(\dfrac{2}{5}\) + \(\dfrac{2}{9}\)

=  \(\dfrac{8}{9}\)  \(\times\) \(\dfrac{7}{5}\) - \(\dfrac{7}{9}\) \(\times\) \(\dfrac{2}{5}\) + \(\dfrac{2\times5}{9\times5}\)

= \(\dfrac{56-14-10}{9\times5}\)

= \(\dfrac{52}{45}\)

Hì hì xin lỗi trả lời muộn thông cảm

S=1+2-3-4+......+993+994-995-996+997+998

=1+(2-3-4+5)+(6-7-8+9)+......+(994-995-996+997)+998

=1+0+0+......+0+998

=999

Mk nhầm rồi = 999

\(\text{S=1+2-3-4+5+6-7-8+9+...+994-995-996+997+998}\)

\(S\text{=1+(2-3-4+5)+(6-7-8+9)+......+(994-995-996+997)+998}\)

\(S\text{=1+0+0+......+0+998}\)

\(S=999\)

a) \(\dfrac{7}{5}x\div\left(9-6\dfrac{13}{21}\right)=2\dfrac{13}{25}\)

\(\dfrac{7}{5}x\div\left(9-\dfrac{139}{21}\right)=\dfrac{63}{25}\)

\(\dfrac{7}{5}x\div\dfrac{50}{21}=\dfrac{63}{25}\)

\(\dfrac{7}{5}x=6\)

\(x=\dfrac{30}{7}\)

b) \(\left(1,16-x\right)\times5,25\div\left(10\dfrac{5}{9}-7\dfrac{1}{4}\right)\times2\dfrac{2}{17}=75\%\)

\(\left(1,16-x\right)\times5,25\div\left(\dfrac{95}{9}-\dfrac{29}{4}\right)\times\dfrac{36}{17}=\dfrac{75}{100}\)

\(\left(1,16-x\right)\times5,25\div\dfrac{119}{36}=\dfrac{17}{48}\)

\(\left(1,16-x\right)\times5,25=\dfrac{2023}{1728}\)

\(1,16-x=\dfrac{289}{1296}\)

\(x=0,9370061728\)

52 ×.(y : 78) = 3380

         y : 78   = 3380 : 52

         y : 78   = 65

         y           = 65 ×. 78

         y           = 5070

hãy trả lời rồi kết bạn với mk nhé

1^3-3^5-(-3^5)+1^64-2^9-1^36+1^15

=1+(-3^5+3^5)+1-2^9-1+1

=2-2^9

=-510