\[\boxed{\mathbf{2.}}\]
\[2)\ НОД(a;b) = 2 \cdot 5 = 10.\]
\[3)\ НОД(a;b) = 2 \cdot 5 = 10.\]
\[4)\ НОД(a;b) = 3 \cdot 7 = 21.\]
\[5)\ НОД(a;b) = 1.\]
\[6)\ НОД(a;b) = 5 \cdot 7 \cdot 11 =\]
\[= 5 \cdot 77 = 385.\]
\[\boxed{\mathbf{3.}}\]
\[1)\ 20\ и\ 35\]
\[НОД(20,\ 35) = 5.\]
\[2)\ 18\ и\ 45\]
\[НОД(18,\ 45) = 3 \cdot 3 = 9\]
\[\mathbf{19.\ Наименьшее\ общее\ кратное}\]