∵ x + y = z
∴ x + y - z = 0
∴ x(a + b - c)- y(c - a - b)- z(b - c + a)
= x(a + b - c)+ y(a + b - c)- z(a + b - c)
= (x + y - z)(a + b - c)
= 0 × (a +b- c)
= 0
∵ x + y = z
∴ x + y - z = 0
∴ x(a + b - c)- y(c - a - b)- z(b - c + a)
= x(a + b - c)+ y(a + b - c)- z(a + b - c)
= (x + y - z)(a + b - c)
= 0 × (a +b- c)
= 0