а) (a+1)(a+4) = a^2 + 4a + a + 4 = a^2 + 5a + 4
б) (x+1)(y+1) = xy + x + y + 1
в) (xy+1)(x+y) = x^2y + xy + x + y
а) (a+1)(a+4) = a^2 + 4a + a + 4 = a^2 + 5a + 4
б) (x+1)(y+1) = xy + x + y + 1
в) (xy+1)(x+y) = x^2y + xy + x + y