a + b = 25 si b + c = 35 ,calculati 3a+6b+c
3a + 6b + 3c = 3a + 3b + 3b + 3c =
3 (a+b) + 3 (b+c) =
3×25 + 3×35 =
75 + 105 =
3a + 6b + 3c = 180
sau
(a + b) + (b + c) = 25 + 35
a + 2b + c = 60 daca inmultim cu 3 ⇒
3a + 6b + 3c = 180 , exact ce ne doream!!!!!