A=1                                                                                                                                                                                                  B=-4

a)

\(11\dfrac{3}{13}-\left(2\dfrac{4}{7}+5\dfrac{3}{13}\right)\)

\(=\dfrac{146}{13}-\left(\dfrac{18}{7}+\dfrac{68}{13}\right)\)

\(=\dfrac{146}{13}-\dfrac{18}{7}-\dfrac{68}{13}\)

\(=\left(\dfrac{146}{13}-\dfrac{68}{13}\right)-\dfrac{18}{7}\)

\(=6-\dfrac{18}{7}\)

\(=\dfrac{24}{7}\)

b)

\(\dfrac{2}{7}\times5\dfrac{1}{4}-\dfrac{2}{7}\times3\dfrac{1}{4}\)

\(=\dfrac{2}{7}\times\dfrac{21}{4}-\dfrac{2}{7}\times\dfrac{13}{4}\)

\(=\dfrac{2}{7}\times\left(\dfrac{21}{4}-\dfrac{13}{4}\right)\)

\(=\dfrac{2}{7}\times2\)

\(=\dfrac{4}{7}\)

\(a,11\dfrac{3}{13}-\left(2\dfrac{4}{7}+5\dfrac{3}{13}\right)\)

\(=\dfrac{146}{13}-\left(\dfrac{18}{7}+\dfrac{68}{13}\right)\)

\(=\dfrac{146}{13}-\dfrac{68}{13}-\dfrac{18}{7}\)

\(=6-\dfrac{18}{7}\)

\(=\dfrac{24}{7}\)

\(b,\dfrac{2}{7}\times5\dfrac{1}{4}-\dfrac{2}{7}\times3\dfrac{1}{4}\)

\(=\dfrac{2}{7}\times\dfrac{21}{4}-\dfrac{2}{7}\times\dfrac{13}{4}\)

\(=\dfrac{2}{7}\times\left(\dfrac{21}{4}-\dfrac{13}{4}\right)\)

\(=\dfrac{2}{7}\times2\)

\(=\dfrac{4}{7}\)

= 5/7.(5/11-2/11-14/4)

=5/7.(-71/22)= -355/154

A=\(\frac{5}{7}\)x\(\frac{5}{11}\)-\(\frac{5}{7}\)x\(\frac{2}{11}\)-\(\frac{5}{7}\)x\(\frac{14}{4}\)

A= \(\frac{5}{7}\)x(\(\frac{5}{11}\)-\(\frac{2}{11}\)-\(\frac{14}{4}\))

A=\(\frac{5}{7}\)x(\(\frac{3}{11}\)-\(\frac{14}{4}\))

A=\(\frac{5}{7}\)x\(\frac{-71}{22}\)

A=\(\frac{-355}{154}\)

a) 

Do `3/2 > 1; 4/3 > 1; 7/6 > 1`

`=> 3/2 + 4/3 + 7/6 > 1+1+1`

`=> 3/2 + 4/3 + 7/6 > 3`

b) 

Do `4/7 < 1; 5/12 <1; 84/87 < 1`

`=> 4/7 + 5/12 + 84/87 < 1+1+1`

`=> 4/7 + 5/12 + 84/87 < 3`

a: \(=\dfrac{4}{5}\cdot\dfrac{7}{3}\cdot\dfrac{3}{7}\cdot\dfrac{5}{4}+2011=2011+1=2012\)

b: \(=\dfrac{1}{3}\cdot\dfrac{9}{7}\cdot\dfrac{7}{9}=\dfrac{1}{3}\)

`a)4/5:3/7xx3/7:4/5+2011`

`=4/5xx7/3xx3/7xx5/4+2011`

`=(4/5xx5/4)xx(7/3xx3/7)+2011`

`=1xx1+2011`

`=1+2011`

`=2012`

__

`b)1/2xx2/3:7/9xx7/9`

`=1/2xx2/3xx9/7xx7/9`

`=(1/2xx2/3)xx(9/7xx7/9)`

`=1/3xx1`

`=1/3`

\(A=\frac{3^2}{1.4}+\frac{3^2}{4.7}+\frac{3^2}{7.10}+...+\frac{3^2}{97.100}\)

\(A=\frac{3^2}{3}\cdot\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+....+\frac{1}{97}-\frac{1}{100}\right)\)

\(A=3\cdot\left(1-\frac{1}{100}\right)\)

\(A=3\cdot\frac{99}{100}=\frac{297}{100}\)

Vậy \(A=\frac{297}{100}\)

\(A=\frac{3}{4}+\frac{2}{7}+\frac{1}{4}+\frac{3}{5}+\frac{5}{7}\)

\(A=\left(\frac{3}{4}+\frac{1}{4}\right)+\left(\frac{2}{7}+\frac{5}{7}\right)+\frac{3}{5}\)

\(A=1+1+\frac{3}{5}\)

\(A=\frac{5}{5}+\frac{5}{5}+\frac{3}{5}\)

\(A=\frac{13}{5}\)

A=(3/4+1/4)+(2/+5/7)+3/5

A= 1+1+3/5

A=13/5

A = ( 3/4 + 1/4 ) + ( 2/7 + 5/7 ) + 3/5

A = 5/4 + 1 + 3/5

A = 25/20 + 1 + 12/20

A = 37/20 + 1

A = 1 và 37/20

\(A=\frac{\frac{2}{3}+\frac{2}{5}-\frac{2}{7}+\frac{2}{91}}{\frac{4}{3}+\frac{4}{5}-\frac{4}{7}+\frac{4}{91}}.\)

\(A=\frac{\frac{2}{3}+\frac{2}{5}-\frac{2}{7}+\frac{2}{91}}{2.\left(\frac{2}{3}+\frac{2}{5}-\frac{2}{7}+\frac{2}{91}\right)}\)

\(A=\frac{1}{2}\)

\(A=\frac{\frac{2}{3}+\frac{2}{5}-\frac{2}{7}+\frac{2}{91}}{\frac{4}{3}+\frac{4}{5}-\frac{4}{7}+\frac{4}{91}}=\frac{\frac{2}{3}+\frac{2}{5}-\frac{2}{7}+\frac{2}{91}}{2.\left(\frac{2}{3}+\frac{2}{5}-\frac{2}{7}+\frac{2}{91}\right)}=\frac{1}{2}\)

Cách này là nhanh nhất rùi

Ủng hộ mk nha ^_-

A=[2/3 + 2/5 - 2/7 + 2/91] / [4/3 + 4/5 - 4/7 +4/91]

  =[2/3 + 2/5 - 2/7 +2/91] / [2.(2/3 + 2/5 - 2/7 + 2/91]

  =                               1/2

1)=90

2)=8330

3)=10

a,4/7

b,5/8

c,7/2

a)2/3*4/7+1/3*4/7=(2/3+1/3)*4/7=1*4/7=4/7

b)5/8*3/7*7/3=5/8*1=5/8

c)(4/5+2)*5/4=4/5*5/4+2=1+2=3

a, 4/7

b,5/8

c, 7/2