(17/28+18/29-19/30-20/31).(-5/12+1/4+1/6)

( $\dfrac{17}{28}$ + $\dfrac{18}{29}$ - $\dfrac{19}{30}$ - $\dfrac{20}{31}$ ) $\times$ ( $\dfrac{-5}{12}$ + $\dfrac{1}{4}$ + $\dfrac{1}{6}$ ) 

= ( $\dfrac{17}{28}$ + $\dfrac{18}{29}$ - $\dfrac{19}{30}$ - $\dfrac{20}{31}$ ) $\times$ ( $\dfrac{-5}{12}$ + $\dfrac{3}{12}$ + $\dfrac{2}{12}$ ) 

= ( $\dfrac{17}{28}$ + $\dfrac{18}{29}$ - $\dfrac{19}{30}$ - $\dfrac{20}{31}$ ) $\times$ $\dfrac{0}{12}$

= ( $\dfrac{17}{28}$ + $\dfrac{18}{29}$ - $\dfrac{19}{30}$ - $\dfrac{20}{31}$ ) $\times$ 0

= 0

Xin hay nhất chúc học tốt ( thử latex )