A(x) = -12x + 18 =0
\(\Leftrightarrow\) -12x = -18
\(\Leftrightarrow\) x = \(\dfrac{3}{2}\)
B(x) = -x2 + 16 = 0
\(\Leftrightarrow\)-x2 = -16
\(\Leftrightarrow\) x = 4
C(x) = 3x2 + 12 = 0
\(\Leftrightarrow\) 3x2 = -12
\(\Leftrightarrow\) x2 = -4
\(\Leftrightarrow\) x \(\in\)\(\varnothing\)