a) 7/19x8/11+7/19x3/11+12/19 b) 9/5x2/7x5/9x(-14) c) -9/16x8/15-7/16x9/15 Giúp mình với. Cảm ơn

a) $\dfrac{7}{19}$ $\times$ $\dfrac{8}{11}$ + $\dfrac{7}{19}$ $\times$ $\dfrac{3}{11}$ + $\dfrac{12}{19}$ 

= $\dfrac{7}{19}$ $\times$ ( $\dfrac{8}{11}$ + $\dfrac{3}{11}$ ) + $\dfrac{12}{19}$ 

= $\dfrac{7}{19}$ $\times$  $\dfrac{11}{11}$ + $\dfrac{12}{19}$ 

= $\dfrac{7}{19}$ $\times$  1 + $\dfrac{12}{19}$ 

= $\dfrac{7}{19}$+ $\dfrac{12}{19}$ 

= $\dfrac{19}{19}$

= 1 

b) $\dfrac{9}{5}$ $\times$ $\dfrac{2}{7}$ $\times$ $\dfrac{9}{5}$ $\times$ ( -14 ) 

= ( $\dfrac{9}{5}$ $\times$ $\dfrac{9}{5}$ ) $\times$  ( -14 ) $\times$ $\dfrac{2}{7}$ ) 

= 1 $\times$ ( -4 ) 

= -4

c) $\dfrac{-9}{16}$ $\times$ $\dfrac{8}{15}$ - $\dfrac{7}{16}$ $\times$ $\dfrac{9}{15}$

= $\dfrac{-72}{240}$ - $\dfrac{63}{240}$

= $\dfrac{-135}{240}$

= $\dfrac{-9}{16}$

Đáp án + Giải thích các bước giải:

`a)`

$\dfrac{7}{19}$ $\times$ $\dfrac{8}{11}$ + $\dfrac{7}{19}$ $\times$ $\dfrac{3}{11}$ + $\dfrac{12}{19}$

`= ( `$\dfrac{7}{19}$ + $\dfrac{12}{9}$ ) $\times$ `(` $\dfrac{8}{11}$ `+` $\dfrac{3}{11}$` )`

`=` $\dfrac{19}{19}$ $\times$ $\dfrac{11}{11}$

`=` $\text{1 $\times$  1 }$

$\text{= 1 }$

`b)`

$\dfrac{9}{5}$ $\times$ $\dfrac{2}{7}$ $\times$ $\dfrac{5}{9}$ $\times$ $\text{(- 14 )}$

= ( $\dfrac{9}{5}$ x $\dfrac{5}{9}$ ) $\times$ ( $\dfrac{2}{7}$ $\times$ $\text{(- 14 )}$

$\text{= 1 $\times$ ( - 4 )}$

$\text{= - 4}$

`c)`

$\dfrac{-9}{16}$ $\times$ $\dfrac{8}{15}$ - $\dfrac{7}{16}$ $\times$ $\dfrac{9}{15}$

$\text{= $\dfrac{-9}{16}$ }$