a)(1/4+3/4)-(5/13+8/13)+2/11=1-1+2/11=2/11

b)(21/31+10/31)-16/7+(44/53+9/53)=1+1-16/7=14/7-16/7=-2/7

bằng2/11

         -16/7

$A=\dfrac{\left(\dfrac15-\dfrac27\right)\cdot\dfrac34-\dfrac34\cdot\left(\dfrac13-\dfrac27\right)}{\dfrac15\cdot\dfrac27-\dfrac13\cdot\left(\dfrac27+\dfrac39\right)+\dfrac39+\dfrac15}$

$=\dfrac{\dfrac34\left[\left(\dfrac15-\dfrac27\right)-\left(\dfrac13-\dfrac27\right)\right]}{\dfrac2{35}-\dfrac13\left(\dfrac27+\dfrac13\right)+\dfrac13+\dfrac15}$

$=\dfrac{\dfrac34\left(\dfrac15-\dfrac13\right)}{\dfrac2{35}-\dfrac13\cdot\dfrac{13}{21}+\dfrac13+\dfrac15}$

$=\dfrac{\dfrac34\cdot\left(-\dfrac2{15}\right)}{\dfrac2{35}-\dfrac{13}{63}+\dfrac{8}{15}}$

$=\dfrac{-\dfrac1{10}}{\dfrac{18-65+168}{315}}$

$=\dfrac{-\dfrac1{10}}{\dfrac{121}{315}}$

$=-\dfrac1{10}\cdot\dfrac{315}{121}$

$=-\dfrac{63}{242}.$

bằng-1/5

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

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

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

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

bằng 4 nha

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

(-5/7+-2/7)+(3/4+1/4)+-1/5

-1+1+-1/5

-1/5

$A=\dfrac{\left(\dfrac15-\dfrac27\right)\cdot\dfrac34-\dfrac34\cdot\left(\dfrac13-\dfrac27\right)}{\dfrac15\cdot\dfrac27-\dfrac13\cdot\left(\dfrac27+\dfrac39\right)+\dfrac39+\dfrac15}$

$=\dfrac{\dfrac34\left[\left(\dfrac15-\dfrac27\right)-\left(\dfrac13-\dfrac27\right)\right]}{\dfrac2{35}-\dfrac13\cdot\left(\dfrac27+\dfrac13\right)+\dfrac13+\dfrac15}$

$=\dfrac{\dfrac34\left(\dfrac15-\dfrac13\right)}{\dfrac2{35}-\dfrac13\cdot\dfrac{13}{21}+\dfrac13+\dfrac15}$

$=\dfrac{\dfrac34\cdot\left(-\dfrac2{15}\right)}{\dfrac2{35}-\dfrac{13}{63}+\dfrac13+\dfrac15}$

$=\dfrac{-\dfrac1{10}}{\dfrac{18-65+105+63}{315}}$

$=\dfrac{-\dfrac1{10}}{\dfrac{121}{315}}$

$=-\dfrac1{10}\cdot\dfrac{315}{121}$

$=-\dfrac{63}{242}.$

a) Hình tròn tâm O,bán kính 3cm

a) Hình tròn tâm O,bán kính 3cm

a) Hình tròn tâm O,bán kính 3cm

a)4200

b)12