Раскрыть скобки и упростить:

1) 7a - (5a+4b)

2) 9x - (7y-4x)

3) - (2a-3b) - (-a+3b)

4) 8x - (3y+5x) - (-2y-x)

1) = 7a - 5a - 4b = (7a - 5a) - 4b = 2a - 4b

2) = 9x - 7y + 4x = (9x + 4x) - 7y = 13x - 7y

3) = - 2a + 3b + a - 3b = (-2a + a) + (3b - 3b) = - a

4) = 8x - 3y - 5x + 2y + x = (8x - 5x + x) - (3y - 2y) = 4x - y