\(a,25\%x=42,6-3,28\\ \Leftrightarrow\dfrac{1}{4}x=39,32\\ \Leftrightarrow x=157,28\)

\(b,x:40\%=7,25+6,75\\ \Leftrightarrow x:40\%=14\\ \Leftrightarrow x=5,6\)

\(c,\dfrac{7011}{25}:\left(x-42,6\right)=117,14-47,03\\ \Leftrightarrow\dfrac{7011}{25}:\left(x-42,6\right)=70,11\\ \Leftrightarrow x-42,6=4\\ \Leftrightarrow x=46,6\)

\(d,0,3\left(x+\dfrac{1}{3}\right)=\dfrac{1}{2}\cdot\left(0,81:27\right)\\ \Leftrightarrow0,3\left(x+\dfrac{1}{3}\right)=0,015\\ \Leftrightarrow x+\dfrac{1}{3}=0,05\\ \Leftrightarrow x=-\dfrac{17}{60}\)

(x+0,2)+(x+0.7)+...+(x+4,7)=65,5

có số x là:(4,7-0,2):0,5+1=10(số)

=> x.10+(0,2+0,7+...+4,7)=65,5

=>x.10+24,5=65,5

=>x.10=65,5-24,5

=>x.10=41

=>x     =41:10

x=4,1

vậy x=1 tí nữa mik làm tiếp cho

(x+0,2)+(x+0.7)+...+(x+4,7)=65,5

có số x là:(4,7-0,2):0,5+1=10(số)

=> x.10+(0,2+0,7+...+4,7)=65,5

=>x.10+24,5=65,5

=>x.10=65,5-24,5

=>x.10=41

=>x     =41:10

x=4,1

vậy x=1

\(\dfrac{7011}{25}:\left(x-42.6\right).15=13\)

\(\Rightarrow\dfrac{7011}{\dfrac{25}{\left(x-42,6\right)}}.0,15=13\)

\(\Rightarrow\dfrac{280,44}{\left(x-42,6\right)}.0,15=13\)

\(x-\left(280,44-42,6\right)\)

\(x=237.8+86,7\)

\(x=324,54\)

\(\)Vậy x=324,54

b.

\(7,2-\left(x+3,75:2,1\right):1,9=5,2\)

\(\Rightarrow7,2+\dfrac{-\left(x-\dfrac{3,75}{2,1}\right)}{1,9}=5,2\)

\(7,2+\dfrac{-\left(x-1,8\right)}{1,9}=5,2\)

Đi đâu cx gặp A.R.M.Y. Hihi. Kb nha

\(\left(\frac{1}{4}.x-\frac{1}{8}\right).\frac{3}{4}=\frac{1}{4}\)

<=> \(\frac{1}{4}x-\frac{1}{8}=\frac{1}{3}\)

<=> \(\frac{1}{4}x=\frac{11}{24}\)

<=> \(x=\frac{11}{6}\)

\(\frac{1}{2}:x+\frac{3}{4}=1\frac{2}{3}\)

<=> \(\frac{1}{2}:x+\frac{3}{4}=\frac{5}{3}\)

<=> \(\frac{x}{2}=\frac{11}{12}\)

=> \(12x=22\)

<=> \(x=\frac{11}{6}\)

\(2x-\frac{3}{7}=\frac{2}{7}+\frac{3}{4}\)

<=> \(2x-\frac{3}{7}=\frac{29}{28}\)

<=> \(2x=\frac{41}{28}\)

<=> \(x=\frac{41}{56}\)

\(25\%.x=42,6-3,28\)

<=> \(0,25x=39,32\)

<=> \(x=157,28\)

\(\frac{15}{12}.x+\frac{3}{7}.x=\frac{6}{5}-\frac{1}{2}\)

<=> \(\left(\frac{15}{12}+\frac{3}{7}\right).x=\frac{7}{10}\)

<=> \(\frac{47}{28}.x=\frac{7}{10}\)

<=> \(x=\frac{98}{235}\)

\(\left(x-\frac{1}{2}\right).\frac{5}{3}=\frac{7}{4}-\frac{1}{2}\)

<=> \(\left(x-\frac{1}{2}\right).\frac{5}{3}=\frac{5}{4}\)

<=> \(x-\frac{1}{2}=\frac{3}{4}\)

<=> \(x=\frac{5}{4}\)

học tốt

j) (x + 2).(3 - x) = 0

TH1:  x + 2 = 0

          x = 0 - 2

          x = (-2)

TH2: 3 - x = 0

              x = 3 - 0

              x = 3

⇒ Vậy x = (-2) hoặc x = 3.

m) (x + 5).(x.2 - 4) = 0

TH1: x + 5 = 0

         x = 0 - 5

         x = (-5)

TH2: x.2 - 4 = 0

         x.2 = 0 + 4

         x.2 = 4

         x = 4 : 2

         x = 2

⇒ Vậy x = (-5) hoặc x = 2.

g) 0,3x + 0,6x = 9

x.(0,3 + 0,6) = 9

x. 0,9 = 9

x = 9 : 0,9

x = 10

j) (x + 2)(3 - x) = 0

x + 2 = 0 hoặc 3 - x = 0

*) x + 2 = 0

x = 0 - 2

x = -2

*) 3 - x = 0

x = 3

Vậy x = -2; x = 3

m) (x + 5)(x.2 - 4) = 0

x + 5 = 0 hoặc x.2 - 4 = 0

*) x + 5 = 0

x = 0 - 5

x = -5

*) x.2 - 4 = 0

2x = 0 + 4

2x = 4

x = 4 : 2

x = 2

Vậy x = -5; x = 2

g) 0,3x + 0,6x = 9

0,9x = 9

x = 9 : 0,9

x = 10

Y÷ 3,5 =14,6 + 2,7

Câu 1 : Áp dụng dấu ngoặc là ra thui bạn tự làm 

Câu 2 : 

\(\left(x+3\right)^2=0,81\)

\(\Leftrightarrow\)\(\orbr{\begin{cases}\left(x+3\right)^2=0,9^2\\\left(x+3\right)^2=\left(-0,9\right)^2\end{cases}\Leftrightarrow\orbr{\begin{cases}x+3=0,9\\x+3=-0,9\end{cases}}}\)

\(\Leftrightarrow\)\(\orbr{\begin{cases}x=0,9-3\\x=-0,9-3\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-2,1\\x=-3,9\end{cases}}}\)

Vậy \(x=-2,1\) hoặc \(x=-3,9\)

Chúc bạn học tốt ~ 

Toán lớp 6 mà có bình phương nữa hả e?

`-(x-42,6+47,03): 27/4=0`

`-[x-(42,6-47,03)]=0`

`-(x+4,43)=0`

`x+4,43=0`

`x=-4,43`