thuc hien phep tinh a-(-1)\21-1\28 b.-3\29-16\58 c.8\40- -36\45 d.-8\18- -15\27 giup em vs

`a, -(-1)/21 - 1/28`

`= 1/21 - 1/28`

`= 4/84 - 3/84`

`= 1/84`

`b, (-3)/29 - 16/58`

`= (-6)/58 - 16/58`

`= -22/58`

`= -11/29`

`c, 8/40 - (-36)/45`

`= 1/5 + 4/5`

`= 5/5 = 1`

`d, (-8)/18 - (-15)/27`

`= -4/9 + 5/9`

`= 1/9`

$\text{a) -$\dfrac{-1}{21}$ - $\dfrac{-1}{28}$}$

$\text{= ( $\dfrac{1}{21}$ + $\dfrac{-1}{28}$ ) }$

$\text{= ( $\dfrac{4}{84}$ + $\dfrac{-3}{84}$ ) }$

$\text{= $\dfrac{1}{84}$}$

$\text{b) $\dfrac{-3}{29}$ - $\dfrac{16}{58}$ }$

$\text{=  $\dfrac{-6}{58}$ - $\dfrac{16}{58}$ }$

$\text{=  -($\dfrac{6}{58}$ +  $\dfrac{16}{58}$ ) }$

$\text{= -$\dfrac{22}{58}$}$

$\text{= $\dfrac{-11}{29}$}$

$\text{c) $\dfrac{8}{40}$ - $\dfrac{-36}{45}$ }$
$\text{=  $\dfrac{1}{5}$ - $\dfrac{-4}{5}$ }$
$\text{=  $\dfrac{1}{5}$ +  $\dfrac{-4}{5}$ }$
$\text{= $\dfrac{5}{5}$ }$

$\text{= 1 }$

$\text{d) $\dfrac{-8}{18}$ - $\dfrac{-15}{27}$ }$
$\text{=  $\dfrac{-4}{9}$ - $\dfrac{-5}{9}$ }$
$\text{=  $\dfrac{1}{9}$ }$