\(\left[12\cdot15-x\right]\cdot\frac{1}{4}=120\cdot\frac{1}{4}\)

\(\Leftrightarrow\left[180-x\right]\cdot\frac{1}{4}=30\)

\(\Leftrightarrow180-x=30:\frac{1}{4}\)

\(\Leftrightarrow180-x=120\)

\(\Leftrightarrow x=60\)

tl moi cau

\(\left[x\cdot0,25+2012\right]\cdot2013=\left[50+2012\right]\cdot2013\)

\(\Leftrightarrow x\cdot0,25\cdot2013+2012\cdot2013=2062\cdot2013\)

\(\Leftrightarrow x\cdot\frac{2013}{4}+4050156=4150806\)

\(\Leftrightarrow x\cdot\frac{2013}{4}=100650\)

\(\Leftrightarrow x=100650:\frac{2013}{4}=100650\cdot\frac{4}{2013}=200\)

Gửi kết bn với mh nhé!

ban ko tra loi ho minh cau nay a 

neu the minh ket ban kieu gi

\(\frac{2}{5}:\frac{3}{7}x\frac{3}{7}:\frac{2}{5}+1999=\)\(\frac{2}{5}x\frac{7}{3}x\frac{3}{7}x\frac{5}{2}+1999=\)\(\left(\frac{2x7x3x5}{5x3x7x2}\right)+1999=\)\(1+1999=2000\)

\(\left(1-\frac{1}{2}\right)x\left(1-\frac{1}{3}\right)x\left(1-\frac{1}{4}\right)x\left(1-\frac{1}{5}\right)\)\(=\left(\frac{2}{2}-\frac{1}{2}\right)\)\(x\left(\frac{3}{3}-\frac{1}{3}\right)\)\(x\left(\frac{4}{4}-\frac{1}{4}\right)\)\(x\left(\frac{5}{5}-\frac{1}{5}\right)\)\(=\frac{1}{2}x\frac{2}{3}x\frac{3}{4}x\frac{4}{5}=\)\(\frac{1x2x3x4}{2x3x4x5}=\frac{1x\left(2x3x4\right)}{\left(2x3x4\right)x5}=\frac{1}{5}\)\(.\)

2/5:3/7 nhân 3/7:2/5+1999

=2/5 nhân 7/3 nhân 3/7nhân 5/2+1999

=14/15 nhân 15/14+1999

=1+1999

=2000

(1-1/2) nhân (1-1/3) nhân (1-1/4) nhân (1-1/5)

=1/2 nhân 2/3 nhân 3/4 nhân 4/5

=24/120

=1/5

x+x+x+82=-2-x

=>x+x+x+x=-2-82

4x=-84

x-84/4

x=-21

(a-b+c-d)-9a+b+c+d)=a-b+c-d-a-b-c-d

=(a-a)-(b+b)+(c-c)-(d-d)

=0-2b+0-2d

=-2b-2d

(-a+b-c)+(a-b)-(a-b+c)

=-a+b-c+a-b-a+b-c

=(-a+a-a)+(b-b+b)-(c+c)

=-a+b-2c

-(a-b-c)+(b-c+d)-(a+b+d)

=-a+b+c+c-c+d-a-b-d

=(-a-a)+(b-b)+(c+c-c)+(d-d)

=-2a+0+c+0

=-2a+c

x+x+x+82=-2-x

      3x+82=-2-x     

       3x+x=-2-82

           4x=-84

   x=-84:4=-21

5.(-40).x=-100

   -200.x=-100

          x=-100:(-200)

          x=0,5

-1.(-3).(-6).x=36

          -18.x=36

                x=36:(-18)

                x=-2

|1-4x|=7

Xảy ra hai trường hợp:1-4x=7=>4x=1-7=-6=>x=-6:4=-1,5

                                    1-4x=-7=>4x=1+7=8=>x=8:4=2

Vì x là số nguyên nên ta chỉ có một đáp án đó là:2

x.(x-2)=0+> x=0 hoặc  x=2

x.(x-2)>0=>x=-1;-2;-3;-4;...

       Câu hỏi của Nguyễn Hữu Hưng       

\(\frac{1}{5.8}+\frac{1}{8.11}+...+\frac{1}{x.\left(x+3\right)}=\frac{101}{1540}\)

\(\frac{3}{5.8}+\frac{3}{8.11}+...+\frac{3}{x.\left(x+3\right)}=\frac{303}{1540}\)

\(\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{x}-\frac{1}{x+3}=\frac{303}{1540}\)

\(\frac{1}{5}-\frac{1}{x+3}=\frac{303}{1540}\)

\(\frac{1}{x+3}=\frac{1}{308}\)

\(\Rightarrow x+3=308\)

\(x=305\)

A ) x = 5/24

B ) x = 7/15