a) \(\dfrac{4}{x}=\dfrac{2}{9}\)

    \(x=\dfrac{\left(4\times9\right)}{2}\)

    \(x=\dfrac{36}{2}\)

   \(x=18\)

b) \(x\times0,3=\dfrac{3}{5}\)

    \(x\times\dfrac{3}{10}=\dfrac{3}{5}\)

    \(x=\dfrac{3}{5}:\dfrac{3}{10}\)

    \(x=\dfrac{3}{5}\times\dfrac{10}{3}\)

    \(x=\dfrac{30}{15}\)

    \(x=2\)

c) \(1,1=\dfrac{3}{4}\) câu này thiếu 

d) \(121,8:x=\dfrac{5}{9}\)

    \(\dfrac{609}{5}:x=\dfrac{5}{9}\)

              \(x=\dfrac{609}{5}:\dfrac{5}{9}\)

              \(x=\dfrac{609}{5}\times\dfrac{9}{5}\)

              \(x=\dfrac{5481}{25}\)

c) \(x:1,1=\dfrac{3}{4}\)

    \(x:\dfrac{11}{10}=\dfrac{3}{4}\)

    \(x=\dfrac{3}{4}\times\dfrac{11}{10}\)

    \(x=\dfrac{33}{40}\)

a, (27,5 x 0,1 + 2,5 x 0,1) x 2

=(0,1 x (2,5+27,5)) x 2

=(0,1 x 30) x 2

=3 x 2

=6

b, 82,37 + 36 + 63 x 82,37 + 82,37

Khó quá ! chắc bạn chép sai đề

c, (27,54 x 1,1 - 279,24 x 0,1) : 0,3

hình nhưu lại sai đề

mik chép đúng mà

thật đấy

Làm hộ mik b2 thôi được ko, mik sẽ tự làm b1 mà

a)\(\dfrac{2}{3}.\dfrac{4}{5}+\dfrac{1}{3}.\dfrac{4}{5}=\left(\dfrac{2}{3}+\dfrac{1}{3}\right).\dfrac{4}{5}=1.\dfrac{4}{5}=\dfrac{4}{5}\)

b)\(\dfrac{2}{3}.\dfrac{4}{5}-\dfrac{1}{3}.\dfrac{4}{5}=\left(\dfrac{2}{3}-\dfrac{1}{3}\right).\dfrac{4}{5}=\dfrac{1}{3}.\dfrac{4}{5}=\dfrac{4}{15}\)

a) \(\dfrac{2}{3}\times\dfrac{4}{5}+\dfrac{1}{3}\times\dfrac{4}{5}=\dfrac{4}{5}\times\left(\dfrac{2}{3}+\dfrac{1}{3}\right)=\dfrac{4}{5}\times1=\dfrac{4}{5}\)

b) \(\dfrac{2}{3}\times\dfrac{4}{5}-\dfrac{1}{3}\times\dfrac{4}{5}=\dfrac{4}{5}\times\left(\dfrac{2}{3}-\dfrac{1}{3}\right)=\dfrac{4}{5}\times\dfrac{1}{3}=\dfrac{4}{15}\)

c) \(\dfrac{1}{2}:\dfrac{3}{4}+\dfrac{1}{6}:\dfrac{3}{4}=\dfrac{1}{2}\times\dfrac{4}{3}+\dfrac{1}{6}\times\dfrac{4}{3}=\dfrac{4}{3}\times\left(\dfrac{1}{2}+\dfrac{1}{6}\right)=\dfrac{4}{3}\times\dfrac{2}{3}=\dfrac{8}{9}\)

d) \(\dfrac{1}{2}:\dfrac{3}{4}-\dfrac{1}{6}:\dfrac{3}{4}=\dfrac{1}{2}\times\dfrac{4}{3}-\dfrac{1}{6}\times\dfrac{4}{3}=\dfrac{4}{3}\left(\dfrac{1}{2}-\dfrac{1}{6}\right)=\dfrac{4}{3}\times\dfrac{1}{3}=\dfrac{4}{9}\)

c)\(\dfrac{1}{2}:\dfrac{3}{4}+\dfrac{1}{6}:\dfrac{3}{4}=\dfrac{1}{2}.\dfrac{4}{3}+\dfrac{1}{6}.\dfrac{4}{3}=\left(\dfrac{1}{2}+\dfrac{1}{6}\right).\dfrac{4}{3}=\dfrac{2}{3}.\dfrac{4}{3}=\dfrac{8}{9}\)

d)\(\dfrac{1}{2}:\dfrac{3}{4}-\dfrac{1}{6}:\dfrac{3}{4}=\dfrac{1}{2}.\dfrac{4}{3}-\dfrac{1}{6}.\dfrac{4}{3}=\left(\dfrac{1}{2}-\dfrac{1}{6}\right).\dfrac{4}{3}=\dfrac{1}{3}.\dfrac{4}{3}=\dfrac{4}{9}\)

a) x : 1/4 = 7/5
    x         = 7/5 x 1/4
    x         = 7/20
b) 9/2 - x = 3/5
            x = 9/2 - 3/5
            x = 39/10
c) 12/5 : x = 7/2
              x = 12/5 : 7/2
              x = 24/35

a) \(x\div\dfrac{1}{4}=\dfrac{7}{5}\)

    \(x=\dfrac{7}{5}\times\dfrac{1}{4}\)

    \(x=\dfrac{7}{20}\)

b) \(\dfrac{9}{2}-x=\dfrac{3}{5}\)

            \(x=\dfrac{9}{2}-\dfrac{3}{5}\)

            \(x=\dfrac{39}{10}\)

c) \(\dfrac{12}{5}\div x=\dfrac{7}{2}\)

             \(x=\dfrac{12}{5}\div\dfrac{7}{2}\)

             \(x=\dfrac{12}{5}\times\dfrac{2}{7}\)

             \(x=\dfrac{24}{35}\)

a)\(x=\dfrac{1}{4}\)x\(\dfrac{7}{5}=\dfrac{7}{20}\)

b)\(x=\dfrac{9}{2}-\dfrac{3}{5}=\dfrac{39}{10}\)

c)\(x=\dfrac{12}{5}:\dfrac{7}{2}=\dfrac{24}{35}\)

OK

1. 1/2-(x-1/4)=1/3

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

=> x-1/4= 1/6

=> x= 1/6+1/4=5/12

2. 3/2*(x-1/2-1)=5/4

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

=> x-1/2= 5/6+1

=> x = 11/6+1/2

=> x= 7/3

3. 11/2-9/2*(x-3/4)=1

=> 9/2*(x-3/4)= 11/2-1

=> x-3/4 = 9/2:9/2

=> x= 1+3/4

=> x= 7/4

Chúc bạn Hk tốt!!!!!

1. x=\(\frac{5}{12}\)

2. x=\(\frac{7}{3}\)

3. x= \(\frac{7}{4}\)

Chúc bạn Hk tốt!!!

bạn làm rõ hơn đc ko cách làm 

a) x² +x +1 = x² + x + 1/4 + 3/4 =(x+1/2)² + 3/4

=> GTNN a) =3/4 khi x=-1/2

b) 4x² +4x -5 = 4x² + 4x +1 -6 = (2x+1)²-6

=> GTNN b) = -6 khi x=-1/2

c) (x-3)(x+5) +4 = x²+2x -11 = x²+2x +1-12=(x+1)²-12

GTNN c) =12 khi x=-1 

d) x²-4x+y²-8y+6=x²-4x+4+y²-8y+16-14=(x-2)²+(y-4)²-14

GTNN d) =-14 khi x=2 , y=4

\(a,=\left(x^2+x+\dfrac{1}{4}\right)+\dfrac{3}{4}=\left(x+\dfrac{1}{2}\right)^2+\dfrac{3}{4}\ge\dfrac{3}{4}\)

Dấu \("="\Leftrightarrow x=-\dfrac{1}{2}\)

\(b,=\left(4x^2+4x+1\right)-6=\left(2x+1\right)^2-6\ge-6\)

Dấu \("="\Leftrightarrow x=-\dfrac{1}{2}\)

\(c,=x^2+2x-15+4=\left(x+1\right)^2-12\ge-12\)

Dấu \("="\Leftrightarrow x=-1\)

\(d,=\left(x^2-4x+4\right)+\left(y^2-8y+16\right)-14=\left(x-2\right)^2+\left(y-4\right)^2-14\ge-14\)

Dấu \("="\Leftrightarrow\left\{{}\begin{matrix}x=2\\y=4\end{matrix}\right.\)

a: \(x\cdot\dfrac{2}{5}+\dfrac{1}{2}\cdot x=9\)

=>\(x\left(\dfrac{2}{5}+\dfrac{1}{2}\right)=9\)

=>\(x\cdot\dfrac{9}{10}=9\)

=>\(x=9:\dfrac{9}{10}=10\)

b: \(\dfrac{1}{9}:x+\dfrac{3}{9}:x=\dfrac{5}{7}\)

=>\(\left(\dfrac{1}{9}+\dfrac{3}{9}\right):x=\dfrac{5}{7}\)

=>\(\dfrac{4}{9}:x=\dfrac{5}{7}\)

=>\(x=\dfrac{4}{9}:\dfrac{5}{7}=\dfrac{4}{9}\cdot\dfrac{7}{5}=\dfrac{28}{45}\)

a: =>x+7/4=6:2/3=9

=>x=29/4

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

=>x=7/5*5/3=7/3

c:=>x+1/6=5/3

=>x=10/6-1/6=3/2

d: =>x+4/5=4/5+3/7+3/5

=>x=3/7+3/5=36/35

e: =>x/35=4/5-5/7=3/35

=>x=3

f: =>13/28+x=1/2

=>x=1/28

g: =>1/3-x=1/9

=>x=2/9