a x=1/4                                                       b x= 3/10

13/23+x=29/30-7/69

13/23+x=199/230

x=199/230-13/23

x=3/10

\(\dfrac{29}{30}-\left(\dfrac{13}{23}+x\right)=\dfrac{7}{69}\)

\(\dfrac{13}{23}+x=\dfrac{29}{30}-\dfrac{7}{69}\)

\(\dfrac{13}{23}+x=\dfrac{2001}{2070}-\dfrac{210}{2070}\)

\(\dfrac{13}{23}+x=\dfrac{1791}{2070}\)

\(x=\dfrac{1791}{2070}-\dfrac{13}{23}\)

\(x=\dfrac{1791}{2070}-\dfrac{1170}{2070}\)

\(x=\dfrac{621}{2070}=\dfrac{3}{10}\)

\(\dfrac{29}{30}-\left(\dfrac{13}{23}+x\right)=\dfrac{7}{69}\)

\(\dfrac{13}{23}+x=\dfrac{29}{30}-\dfrac{7}{69}\)

\(\dfrac{13}{23}+x=\dfrac{199}{230}\)

\(x=\dfrac{13}{23}-\dfrac{199}{230}\)

\(x=\dfrac{-3}{10}\)

a) \(x+\frac{7}{12}=\frac{17}{18}-\frac{1}{9}\)

\(\Rightarrow x+\frac{7}{12}=\frac{5}{6}\)

\(\Rightarrow x=\frac{5}{6}-\frac{7}{12}\)

\(\Rightarrow x=\frac{1}{4}\)

b) \(\frac{29}{30}-\left(\frac{13}{23}+x\right)=\frac{7}{69}\)

\(\Rightarrow\frac{13}{23}+x=\frac{29}{30}-\frac{7}{69}\)

\(\Rightarrow\frac{13}{23}+x=\frac{199}{230}\)

\(\Rightarrow x=\frac{199}{230}-\frac{13}{23}\)

\(\Rightarrow x=\frac{3}{10}\)

a)\(x+\frac{7}{12}=\frac{17}{18}-\frac{1}{9}\)

\(x+\frac{7}{12}=\frac{5}{6}\)

\(x=\frac{5}{6}-\frac{7}{12}\)

\(x=\frac{1}{4}\)

b)\(\frac{29}{30}-\left(\frac{13}{23}+x\right)=\frac{7}{69}\)

\(\left(\frac{13}{23}+x\right)=\frac{29}{30}-\frac{7}{69}\)

\(\left(\frac{13}{23}+x\right)=\frac{199}{230}\)\(x=\frac{199}{230}-\frac{13}{23}\)

\(x=\frac{3}{10}\)

a.X+7/12=17/18-1/9

X+7/12=15/18

X=15/18-7/12

X=1/4

b.29/30-(13/23+X)=7/69

13/23+X=7/69+29/30

13/23+X=737/690

X=737/690-13/23

X=377/690

Tìm x biết:

\(\frac{x}{3}-\frac{3}{4}=\frac{1}{12}\)

\(\frac{x}{3}=\frac{1}{12}+\frac{3}{4}\)

\(\frac{x}{3}=\frac{5}{6}\)

\(x=\frac{5}{6}.3\)

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

Vậy \(x=\frac{5}{2}\)

\(\frac{29}{30}-\left(\frac{13}{23}+x\right)=\frac{7}{69}\)

\(\frac{13}{23}+x=\frac{29}{30}-\frac{7}{69}\)

\(\frac{13}{23}+x=\frac{199}{230}\)

\(x=\frac{199}{230}-\frac{13}{23}\)

\(x=\frac{3}{10}\)

Vậy \(x=\frac{3}{10}\)

Bài 2: tính

\(\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}+\frac{1}{110}\)

\(=\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}+\frac{1}{10.11}\)

\(=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}+\frac{1}{9}-\frac{1}{10}+\frac{1}{10}-\frac{1}{11}\)

\(=\frac{1}{5}-\frac{1}{11}\)

\(=\frac{6}{55}\)

\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{49.50}\)

\(=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{49}-\frac{1}{50}\)

\(=\frac{1}{1}-\frac{1}{50}\)

\(=\frac{49}{50}\)

Bài 2:

1/30+1/42+1/56+1/72+1/90+1/110

=1/5.6+1/6.7+1/7.8+1/8.9+1/9.10+1/10.11

=1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11

=1/5-1/11=6/55

b)1/1.2+1/2.3+...+1/49.50

=1-1/2+1/2-1/3+...+1/49-1/50

=1-1/50

=49/50

a) \(\frac{29}{30}\)- (\(\frac{13}{23}\)+X)=\(\frac{7}{69}\)

\(\frac{13}{23}\)+X=\(\frac{29}{30}\)-\(\frac{7}{69}\)

\(\frac{13}{23}\)+X=\(\frac{199}{230}\)

X=\(\frac{199}{230}\)-\(\frac{13}{23}\)

X=\(\frac{3}{10}\)

b)1/2+1/6+1/12+...+1/x(x+1)=2011/2012

=>1/1.2+1/2.3+1/3.4+...+1/x(x+1)=2011/2012

=>1-1/2+1/2-1/3+1/3+1/4+...+1/x+1/x+1=2011/2012

=>1-1/x+1=2011/2012

=>1/x+1=1-2011-2012

=>1/x+1=2012/2012-2011/2012

1/x+1=1/2012

=>x+1=2012

=>x=2011

a) 3/10

Bài 1: Tìm x biết:

1) x +\(\frac{7}{12}\)= \(\frac{17}{18}\)- \(\frac{1}{9}\)                                                                               2) \(\frac{29}{30}\)- (\(\frac{13}{23}\)+ x) = \(\frac{7}{69}\)

 x +\(\frac{7}{12}\)= \(\frac{15}{18}\)                                                                                                                \(\frac{13}{23}\)+ x = \(\frac{29}{30}\)- \(\frac{7}{69}\)

             x = \(\frac{15}{18}\)- \(\frac{7}{12}\)                                                                                                    \(\frac{13}{23}\)+ x = \(\frac{199}{230}\)

             x = \(\frac{1}{4}\)                                                                                                                                   x = \(\frac{3}{10}\)

1

x + 7/12= 15/18

x= 15/18-7/12

x= 1/4

k mk nhé

3

4/10= 2/5

\(\frac{x}{15}\)=\(\frac{2}{5}\)

x= 15:5x2= 6

x= 6

k mk nhé

a, x + 7/12 = 17/18 - 1/9

    x + 7/12 = 15/18

                x = 15/18 - 7/12

                  x = 1/4

b, 29/30 - ( 13/23 + x ) = 7/69

( 13/23 + x ) = 29/30 - 7/69

13/23 + x = 199/230

              x = 199/230 - 13/23

                x = 3/10

hok tốt