\[\mathbf{Страница\ 53.}\]
\[\boxed{\mathbf{2.}}\]
\[3 \cdot 21 \rightarrow +\]
\[( - 6) \cdot ( - 8) \rightarrow +\]
\[( - 7) \cdot 9 \rightarrow -\]
\[4 \cdot ( - 5) \rightarrow -\]
\[( - 5) \cdot 25 \rightarrow -\]
\[( - 13) \cdot ( - 10) \rightarrow +\]
\[3 \cdot ( - 6) \rightarrow -\]
\[14 \cdot 2 \rightarrow +\]
\[\boxed{\mathbf{3.}}\]
\[\textbf{а)}\ 5 \cdot 9 = 45\]
\[( - 4) \cdot ( - 6) = 24\]
\[( - 7) \cdot 20 = - 140\]
\[\textbf{б)}\ ( - 7) \cdot ( - 3) = 21\]
\[2 \cdot ( - 8) = - 16\]
\[( - 3) \cdot ( - 9) = 27\]
\[\textbf{в)}\ 12 \cdot 5 = 60\]
\[( - 11) \cdot 6 = - 66\]
\[( - 15) \cdot 3 = - 45\]
\[\textbf{г)}\ ( - 5) \cdot 8 = - 40\]
\[( - 9) \cdot ( - 7) = 63\]
\[3 \cdot ( - 6) = - 18\]
\[\textbf{д)}\ ( - 7) \cdot 9 = - 63\]
\[25 \cdot 4 = 100\]
\[44 \cdot ( - 1) = - 44\]
\[\textbf{е)}\ ( - 13) \cdot 6 = - 78\]
\[( - 16) \cdot ( - 5) = 80\]
\[15 \cdot ( - 8) = - 120\]
\[\boxed{\mathbf{4.}}\]
\[7 \cdot ( - 9) = ( - 7) \cdot 9\]
\[( - 5) \cdot ( - 6) = ( - 10) \cdot ( - 3)\]
\[5 \cdot 8 = ( - 8) \cdot ( - 5)\]
\[( - 9) \cdot 5 = 9 \cdot ( - 5)\]
\[\boxed{\mathbf{5.}}\]
\[\textbf{а)}\ 8 \cdot ( - 3) = - 24\]
\[5 \cdot ( - 10) = - 50\]
\[1 \cdot ( - 1) = - 1\]
\[( - 4) \cdot ( - 9) = 36\]
\[( - 13) \cdot ( - 10) = 130\]
\[\textbf{б)} - 9 \cdot 4 = - 36\]
\[- 9 \cdot 10 = - 90\]
\[- 1 \cdot 1 = - 1\]
\[( - 14) \cdot ( - 6) = 84\]
\[( - 19) \cdot ( - 8) = 162\]
\[\textbf{в)}\ 8 \cdot 0 = 0\]
\[- 8 \cdot 8 = - 64\]
\[11 \cdot ( - 5) = - 55\]
\[( - 17) \cdot ( - 7) = 119\]
\[( - 24) \cdot ( - 5) = 120\]