\[Страница\ 13.\]
\[\boxed{\mathbf{5}.}\]
\[2\ см\ и\ 8\ см:\]
\[2 + 8 = 10\ см;\]
\[8 - 2 = 6\ см.\]
\[\boxed{\mathbf{6}.}\]
\[AB = 8\ см.\]
\[\textbf{а)}\ \]
\[\textbf{б)}\ \]
\[\textbf{в)}\ \]
\[\textbf{г)}\ \]
\[\boxed{\mathbf{7}.}\]
\[AB = DC = 25\ мм;\]
\[BC = AD = 15\ мм.\]
\[P = 2 \cdot (25 + 15) = 2 \cdot 40 =\]
\[= 80\ мм = 8\ см.\]
\[Ответ:8\ см.\]