2) $$(y + 3)(y + 1) = y^2 + y + 3y + 3 = y^2 + 4y + 3$$
3) $$(x + 2)(y - 1) = xy - x + 2y - 2$$
4) $$(a + x)(a - y) = a^2 - ay + ax - xy$$
5) $$(a - b)(a - b) = a^2 - ab - ab + b^2 = a^2 - 2ab + b^2$$
Ответ: 2) $$y^2 + 4y + 3$$, 3) $$xy - x + 2y - 2$$, 4) $$a^2 - ay + ax - xy$$, 5) $$a^2 - 2ab + b^2$$