A) 2a ─ ac ─ 2c + c 2 ; б) bx + by - x - y - ax - ay
a) 2a ─ ac ─ 2c + c = (2a-ac) - (2c+c) = a(2-c) - c(2-1)
б) bx + by - x - y - ax - ay = (bx-x) + (by-y) - (ax-ay) = x(b-1) + y(b-1) - a(x+y) = (x+y) (b-1) - a(x+y)