\[\boxed{\text{19\ (19).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
Пояснение.
Решение.
\[\textbf{а)}\ при\ x\ = \ 7:\]
\[4x\ - \ 12\ = \ 4 \cdot 7\ - \ 12\ = \ \]
\[= 28\ - \ 12\ = \ 16.\]
\[при\ x\ = \ 0:\]
\[4x\ - \ 12\ = \ 4 \cdot 0\ - \ 12\ =\]
\[= \ 0\ - \ 12\ = \ - 12.\ \]
\[при\ x\ = \ - 5:\]
\[4x\ - \ 12\ = \ 4\ \cdot ( - 5) - \ 12\ = \ \]
\[= - 20\ - \ 12\ = \ - 32.\]
\[\textbf{б)}\ при\ y\ = \ 3:\]
\[2,8\ - \ 0,5y\ = \ 2,8\ - \ 0,5 \cdot 3\ =\]
\[= \ 2,8\ - \ 1,5\ = \ 1,3.\]
\[при\ y\ = \ 0:\]
\[2,8\ - \ 0,5y\ = \ 2,8\ - \ 0,5 \cdot 0\ = \ \]
\[= 2,8\ - \ 0\ = \ 2,8.\]
\[при\ y\ = \ - 6:\]
\[2,8\ - \ 0,5y\ = \ \]
\[= 2,8\ - \ 0,5 \cdot ( - 6) =\]
\[= \ 2,8\ + \ 3\ = \ 5,8.\]