1. а) \[ 7a + 5a - a = (7+5-1)a = 11a \]
1. б) \[ 11x - 8x + x = (11 - 8 + 1)x = 4x \]
1. в) \[ 13x + x - 12x = (13 + 1 - 12)x = 2x \]
1. г) \[ a - 5a + 10a = (1 - 5 + 10)a = 6a \]
1. д) \[ -7a + 7a + 5a = (-7 + 7 + 5)a = 5a \]
1. е) \[ -5x + 9x - x = (-5 + 9 - 1)x = 3x \]
Ответ: