Sum of 5x + 7y – 12 and 3x – 5y + 2.
= 5x + 7y – 12 + 3x – 5y + 2
= (5x + 3x) + (7y – 5y) + (– 12 + 2)
= 8x + 2y – 10.
Again Sum of 2x – 7y – 1 and – 6x + 3y + 9
= 2x – 7y – 1 + (– 6x) + 3y + 9
= 2x – 7y – 1 – 6x + 3y + 9
= (2x – 6x) + (– 7y + 3y) + (– 1 + 9)
= (– 4x) + (– 4y) + 8
= - 4x - 4y – 8
Now
8x + 2y – 10 – (– 4x – 4y + 8)
= 8x + 2y – 10 + 4x + 4y – 8
= (8x + 4x) + (2y + 4y) + (– 10 + (– 8))
= 12x + 6y + (– 10 – 8)
= 12x + 6y + (-18)
= 12x + 6y -18