2 x + 9 y + 18 z = 185
=( x + x ) + ( 3 y + 3 y + 3 y ) + 18 z =
= ( x + 3 y ) + ( x + 3 y ) + ( 3 y + 18 z ) =
= 28 + 28 + 129 =
= 185
______________________
sau:
2 x + 6 y + 3 y + 18 z = 2 ( x + 3 y ) + ( 3 y + 18 z ) = 2 x 28 + 129 = 56 + 129 = 185