(12x2 +12x4 - 12x6) : (2+4+6+....+18+20)
=12 x (2+4-6) : (2+4+6+...+18+20)
=12 x 0 : (2+4+6+...+18+20)
= 0
= ( 12 . 2 + 12 . 4 - 12 . 6 ) : ( 2+4+6+8+...+18+20)
= 12 . ( 2+4-6 ) : ( 2+4+6+8+...+18+20 )
= 12 . 0 : ( 2+4+6+8+...+18+20 )
= 0
thích cho mình nha !