255 - 21 . 5 . ( 198 : 11 - 8 )
= 255 - 105 . ( 18 - 8 )
= 255 - 105 . 10
= 255 - 1050
= -795
720 : [ 41 - ( 2 . x . 5 ) ] = 23 . 5
720 : [ 41 - ( 10 . x ) ] = 40
41 - ( 10 . x ) = 720 : 40
41 - ( 10 . x ) = 18
10 . x = 41 - 18
10 . x = 23
x = 23/10
Tinh nhanh ( neu co ) :
255 - 21 . 5 . ( 198 : 11 - 8 )
= 255 - 21 . 5 . ( 18 - 8 )
=255 - 21 . 5 . 10
=255 - 1050
= -795