\[\boxed{\text{677\ (677).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
Пояснение.
Решение.
\[\textbf{а)}\ (x + m)(y + n) =\]
\[= xy + xn + my + mn\]
\[\textbf{б)}\ (a - b)(x + y) =\]
\[= ax + ay - bx - by\]
\[\textbf{в)}\ (a - x)(b - y) =\]
\[= ab - ay - xb + xy\]
\[\textbf{г)}\ (x + 8)(y - 1) =\]
\[= xy - x + 8y - 8\]
\[\textbf{д)}\ (b - 3)(a - 2) =\]
\[= ab - 2b - 3a + 6\]
\[\textbf{е)}\ ( - a + y)( - 1 - y) =\]
\[= a + ay - y - y^{2}\]