5/9 x a/b -11/21 = 4/21

\(\dfrac{5}{9}\times\dfrac{a}{b}=\dfrac{4}{21}+\dfrac{11}{21}\)

\(\dfrac{5}{9}\times\dfrac{a}{b}=\dfrac{15}{21}=\dfrac{5}{7}\)

\(\dfrac{a}{b}=\dfrac{5}{7}:\dfrac{5}{9}\)

\(\dfrac{a}{b}=\dfrac{5}{7}\times\dfrac{9}{5}\)

\(\dfrac{a}{b}=\dfrac{9}{7}\)

5/9.a/b=4/21+11/21

5/9.a/b=15/21

a/b=15/21:5/9

a/b=15/21.9/5

a/b=9/7

=> a=9 ; b=7

Bài 1:

a) \(\frac{16}{15}.\frac{\left(-5\right)}{14}.\frac{54}{24}.\frac{56}{21}\)

\(=\frac{4.2.2}{5.3}.\frac{\left(-5\right)}{2.7}.\frac{3.3}{4}.\frac{8}{3}\)

\(=\frac{4.2.2.\left(-5\right).3.3.8}{5.3.2.7.4.3}\)

\(=\frac{-16}{7}\)

b) \(\frac{7}{3}.\frac{\left(-5\right)}{2}.\frac{15}{21}.\frac{4}{\left(-5\right)}\)

\(=\frac{7}{3}.\frac{\left(-5\right)}{2}.\frac{5}{7}.\frac{2.2}{\left(-5\right)}\)

\(=\frac{7.\left(-5\right).5.2.2}{3.2.7.\left(-5\right)}\)

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

Bài 2:

a) \(\frac{21}{24}.\frac{11}{9}.\frac{5}{7}=\frac{7}{8}.\frac{11}{9}.\frac{5}{7}=\frac{11.5}{8.9}=\frac{55}{72}\)

b) \(\frac{5}{23}.\frac{17}{26}+\frac{5}{23}.\frac{9}{26}\)

\(=\frac{5}{23}.\left(\frac{17}{26}+\frac{9}{26}\right)=\frac{5}{23}.1=\frac{5}{23}\)

c) \(\left(\frac{3}{29}-\frac{1}{5}\right).\frac{29}{3}=\frac{3}{29}.\frac{29}{3}-\frac{1}{5}.\frac{29}{3}\)

\(=1-1\frac{14}{15}=\frac{14}{15}\)

Bài 3:

a) x/5 = 2/5

=> x =2

b) -4/x = 20/14 = 10/7

=> -4/x = 10/7

=> x.10 = (-4).7

x.10 = - 28

x= -28 :10

x= -2,8

c) 4/7 = 12/x = 12/ 21

=> 12/x = 12/21

=> x = 21

d) 3/7 = x / 21 = 9/21

=> x/21 = 9/21

=> x= 9

\(\frac{5}{9}\) . \(\frac{a}{b}\) - \(\frac{11}{21}\) = \(\frac{4}{21}\)  

\(\frac{5}{9}\) . \(\frac{a}{b}\)               = \(\frac{4}{21}\) + \(\frac{11}{21}\)

\(\frac{5}{9}\) . \(\frac{a}{b}\)               = \(\frac{5}{7}\) 

            \(\frac{a}{b}\)               = \(\frac{5}{7}\) : \(\frac{5}{9}\) 

              \(\frac{a}{b}\)             = \(\frac{9}{7}\) 

Vậy \(\frac{a}{b}\) = \(\frac{9}{7}\) 

5/9 x a/b-11/21=4/21

<=> 5/9 x a/b=4/21+11/21

<=> 5/9 x a/b = 21/21=1

<=> a/b = 1 : 5/9

<=> a/b=9/5

Vậy a/b=9/5

Ta có : 

\(\frac{5}{9}\times\frac{a}{b}-\frac{11}{21}=\frac{4}{21}\)

\(\Rightarrow\frac{5}{9}\times\frac{a}{b}=\frac{4}{21}+\frac{11}{21}\)

\(\Rightarrow\frac{5}{9}\times\frac{a}{b}=\frac{15}{21}\)

\(\Rightarrow\frac{a}{b}=\frac{15}{21}:\frac{5}{9}\)

\(\Rightarrow\frac{a}{b}=\frac{15}{21}\times\frac{9}{5}\)

\(\Rightarrow\frac{a}{b}=\frac{9}{7}\)

Vậy \(\frac{a}{b}=\frac{9}{7}\)

~ Ủng hộ nhé 

Lời giải:
a.

$x=\frac{7}{25}+\frac{-1}{5}=\frac{7}{25}+\frac{-5}{25}=\frac{7-5}{25}=\frac{2}{25}$

b.

$x=\frac{5}{11}+\frac{4}{-9}=\frac{5}{11}-\frac{4}{9}=\frac{45}{99}-\frac{44}{99}=\frac{1}{99}$

c.

$\frac{x}{-1}=\frac{-1}{3}-\frac{5}{9}=\frac{-3}{9}-\frac{5}{9}=\frac{-8}{9}$

$x=(-1).\frac{-8}{9}=\frac{8}{9}$

\(a.=-2-\left(-5\right)-3+15-12\)

\(=3-3+15-12\)

\(=3\)

\(b.=-9-\left(-5\right)+\left(-21\right)-\left(-3\right)+\left(-11\right)-\left(-7\right)+\left(-4\right)\)

\(=-30\)

a,9-11+5-3+15-12=3

b.-9+5-21+3-11+7-4=-30

1.Tính:

a. 9-11+5-3+15-12=3

b. -9+5-21+3-11+7-4=-30

a) 35

b) -53

c) 40 –  - 7 2  = 40 – 49 = -9

d)| -15 + 21| - | 4 – 11 | = | 6 | - | -7 | = 6 – 7 = -1

a, = \(\frac{11}{21}\)x \(\left(\frac{7}{4}+\frac{5}{4}\right)\)

   = \(\frac{11}{21}\)x 3

  = \(\frac{33}{21}\)

b) = \(\left(\frac{23}{14}-\frac{9}{14}\right)\)x \(\frac{6}{13}\)

    = 1 x \(\frac{6}{13}\)

    = \(\frac{6}{13}\)

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