-2 [4 (a-b)-3 (b-7a)]+(a-b)•50=
-2 [4 (a-b)-3 (b-7a)]+(a-b)•50
= -2 [4 a - 4 b -3 b + 21 a] + (a - b) • 50
= -2 [25 a - 7 b] + (a - b) • 50
= -50 a + 14 b + 50 a - 50 b
= -36 b
= -2 [4 a - 4 b -3 b + 21 a] + (a - b) • 50
= -2 [25 a - 7 b] + (a - b) • 50
= -50 a + 14 b + 50 a - 50 b
= -36 b