1: Áp dụng tính chất của DTSBN, ta được:

\(\dfrac{x}{7}=\dfrac{y}{13}=\dfrac{x-y}{7-13}=\dfrac{42}{-6}=-7\)

=>x=-48; y=-91

2: x/y=3/4

=>4x=3y

=>4x-3y=0

mà 2x+y=10

nên x=3 và y=4

3: =>7x-3y=0 và x-y=-24

=>x=18 và y=42

4: =>7x-5y=0 và x+y=24

=>x=10 và y=14

a) y + 3/7 x 21/9 = 5

      y + 3/7 x 7/3 = 5

      y + 1             = 5

            y             = 4

b) y  x 3/5 - 1/2 = 4/5

    y x 3/5          = 4/5 + 1/2

    y x 3/5          = 13/10

    y                   = 13/6

c) 9/8 - y + 2/5 = 1/4

            y - 2/5  = 9 /8 - 1/4

            y - 2/5  = 7/8

                   y   = 51/40 

d) y - 6/5 : 2/3 = 5/6

    y - 9/5         = 5/6

          y           = 79/30

e) y : 7/8 + 3/4 = 7/4

    y : 7/8          = 1

          y            = 7/8

\(y+\frac{3}{7}\times\frac{21}{9}=5\)

\(y+\frac{3}{7}\times\frac{7}{3}=5\)

\(y+1=5\)

\(\Rightarrow y=4\)

a, \(y=\dfrac{7}{11}-\dfrac{5}{14}=\dfrac{98-55}{154}=\dfrac{43}{154}\)

b, \(y=\dfrac{8}{9}.\dfrac{4}{7}=\dfrac{32}{63}\)

a, \(\frac{2}{5}\)+ y = 1

                y = 1 - \(\frac{2}{5}\)

                y = \(\frac{3}{5}\)

b, \(\frac{6}{8}\)- y = \(\frac{3}{5}\)

               y = \(\frac{6}{8}\)- \(\frac{3}{5}\)

               y = \(\frac{3}{20}\)

c, y : 6 = \(\frac{7}{4}\)

         y = \(\frac{7}{4}\)x 6

         y = \(\frac{21}{2}\)

d, y - \(\frac{1}{3}\)= 5 x \(\frac{2}{3}\)

    y - \(\frac{1}{3}\)= \(\frac{10}{3}\)

           y      = \(\frac{10}{3}\)+ \(\frac{1}{3}\)

           y      = \(\frac{11}{3}\)

a,2/5 + y = 1

            y = 1 - 2/5

            y = 3/5

b, 6/8 - y = 3/5

            y = 6/8 - 3/5

            y = 3/10

c, y / 6 = 7/4 

         y = 7/4 * 6

         y = 15/2

d, y - 1/3 = 5 * 2/3

    y - 1/3 = 10/3

            y = 10/3 + 1/3

            y = 11/3

a ,\(\frac{2}{5}+y=1\)

\(y=1-\frac{2}{5}\)

\(y=\frac{3}{5}\)

b ,\(\frac{6}{8}-y=\frac{3}{5}\)

\(y=\frac{6}{8}-\frac{3}{5}\)

\(y=\frac{6}{40}\)

c,\(\frac{y}{6}=\frac{7}{4}\)

\(=>y=14\)

\(\frac{y}{6}=\frac{7}{4}\)

d,\(y-\frac{1}{3}=5\cdot\frac{2}{3}\)

\(y-\frac{1}{3}=\frac{7}{3}\)

\(y=\frac{7}{3}-\frac{1}{3}\)

\(y=\frac{6}{3}=2\)

Hok tốt#

a) 

\(\left(x+1\right)\left(y-2\right)=5\\ \Rightarrow\left(x+1\right),\left(y-2\right)\inƯ\left(5\right)=\left\{1;-1;5;-5\right\}\)

Ta có bảng:

Vậy \(\left(x;y\right)=\left(0;7\right),\left(-2;-3\right),\left(4;3\right),\left(-6;1\right)\)

b) 

\(\left(x-5\right)\left(y+4\right)=-7\\ \Rightarrow\left(x-5\right),\left(y+4\right)\inƯ\left(-7\right)=\left\{1;-1;7;-7\right\}\)

Ta có bảng:

Vậy \(\left(x;y\right)=\left(6;-11\right),\left(4;3\right),\left(12;-5\right),\left(-2;-3\right)\)

e) 

\(x-\left(17-8\right)=5+\left(10-3x\right)\\ \Rightarrow x-9=5+10-3x\\ \Rightarrow x+3x=5+10+9\\ \Rightarrow4x=24\\ \Rightarrow x=\dfrac{24}{4}=6\)

Vậy \(x=6\)

a)y=5/6

b)y=11/4

\(a\left(\frac{1}{2}-\frac{1}{4}+....+\frac{1}{8}-\frac{1}{10}\right).y=\frac{1}{3}\)
\(\left(\frac{1}{2}-\frac{1}{10}\right).y=\frac{1}{3}\)

\(\frac{2}{5}.y=\frac{1}{3}\)

      \(y=\frac{1}{3}:\frac{2}{5}\)

     \(y=\frac{5}{6}\)

\(b,\left(\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+....+\frac{1}{9}-\frac{1}{11}\right).y=\frac{2}{3}\)

     \(\left(\frac{1}{1}-\frac{1}{11}\right).y=\frac{2}{3}\)

      \(\frac{10}{11}.y=\frac{2}{3}\)

              \(y=\frac{2}{3}:\frac{10}{11}\)

               \(y=\frac{22}{30}\)

a) 3/4*41/24=41/32

B)  y=4/7:3/5

y=20/21

a)3/4 × (5/6 + 7/8)

=3/4 × 41/24

=41/32

b)3/5 × y=4/7

  y=4/7:3/5

          y=20/21