\[x^{2} - ax + 6 = 0\]
\[2^{2} - a \cdot 2 + 6 = 0\]
\[4 - 2a + 6 = 0\]
\[10 - 2a = 0\]
\[2a = 10\]
\[a = 5.\]
\[Ответ:при\ a = 5.\]