\[6bc = 12\ \ \]
\[bc = 2\ \ \]
\[b = 1;\ \ \ \ c = 2.\]
\[6bc = - 60\ \ \]
\[bc = - 10\]
\[b = - 2;\ \ c = 5.\]
\[6bc = 0\ \]
\[bc = 0\]
\[b = 3;\ c = 0.\]
\[6bc = 3\ \ \]
\[bc = \frac{1}{2}\text{\ \ }\]
\[b = 2;\ \ c = \frac{1}{4}.\]