\[Страница\ 27.\]
\[12.\ Действие\ умножения.\ \]
\[Свойства\ умножения\]
\[\boxed{\mathbf{1}.}\]
\[\textbf{а)}\ a \cdot 4\]
\[\textbf{б)}\ 9 \cdot 5\]
\[\textbf{в)}\ (b + 3) \cdot 5\]
\[\boxed{\mathbf{2}.}\]
\[\textbf{а)}\ a \cdot 4 = a + a + a + a\]
\[\textbf{б)}\ (x + y - 3) \cdot 2 =\]
\[= (x + y - 3) + (x + y - 3)\]
\[\boxed{\mathbf{3}.}\]
\[\textbf{а)}\]
\[\textbf{б)}\]
\[\textbf{в)}\]
\[\textbf{г)}\]
\[\textbf{д)}\]
\[\textbf{е)}\ \]