а) (x+2y)+(-x+4y) = x - x + 2y + 4y = 6y
б) (a+b-c)+(a-b-c) = a + b - c + a - b - c = 2a - 2c
в) (a+2)+(a^2-1)+(-a^2+1) = a + 2 + a^2 - 1 - a^2 + 1 = a + a = 2a
г) (m^2-3m)+(-m-3)+(-m^2+4m) = m^2 - 3m - m - 3 - m^2 + 4m = 0
а) (x+2y)+(-x+4y) = x - x + 2y + 4y = 6y
б) (a+b-c)+(a-b-c) = a + b - c + a - b - c = 2a - 2c
в) (a+2)+(a^2-1)+(-a^2+1) = a + 2 + a^2 - 1 - a^2 + 1 = a + a = 2a
г) (m^2-3m)+(-m-3)+(-m^2+4m) = m^2 - 3m - m - 3 - m^2 + 4m = 0