16.
[tex]\it +8=8\in\mathbb{N}\subset \mathbb{Z}\\ \\ +4=4\in\mathbb{N}\subset \mathbb{Z}\\ \\ -(-10)=+10=10\in\mathbb{N}\subset \mathbb{Z}\\ \\ 0\in\mathbb{N}\subset \mathbb{Z}\\ \\ -4\in\mathbb{Z}\\ \\ -41\in\mathbb{Z}\\ \\ \\ M\cap \mathbb{N}=\{0,\ 4,\ 8,\ 10\}\\ \\ M\cap \mathbb{Z}=\{-41,\ -4,\ 0,\ 4,\ 8,\ 10\}[/tex]
20.
[tex]\it \ \ \ \ \ \ \ \ C\ \ \ \ \ \ A\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ O \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ B \\. \ \ \ \ \ \ \ \ |\rule{10}{0.7}|\rule{10}{0.7}|\rule{10}{0.7}|\rule{10}{0.7}|\rule{10}{0.7}|\rule{10}{0.7}|\rule{10}{0.7}|\rule{10}{0.7}|\rule{10}{0.7}|\rule{10}{0.7}|\rule{10}{0.7}|\rule{10}{0.7}|\rule{10}{0.7}|\rule{10}{0.7}|\\.\ \ \ \ -8\ \ \ -6\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 0\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 6[/tex]
AB= 6+6 = 12cm
BC= 8+6 = 14cm
