б) 15a - (a + 3) + (2a - 1) =15a - a - 3 + 2a - 1 =16a - 4
в) 5a - (6a - (7a - (8a - 9))) =5a - (6a - (7a - 8a + 9)) =5a - (6a - (-a + 9)) =5a - (6a + a - 9) =5a - 7a + a + 9 =-2a + a + 9 =-a + 9
б) 15a - (a + 3) + (2a - 1) =
15a - a - 3 + 2a - 1 =
16a - 4
в) 5a - (6a - (7a - (8a - 9))) =
5a - (6a - (7a - 8a + 9)) =
5a - (6a - (-a + 9)) =
5a - (6a + a - 9) =
5a - 7a + a + 9 =
-2a + a + 9 =
-a + 9