Find the values of `a` for which are vectors ` vecalpha= hat i+2 hat j+ hat k , vecbeta=a hat i+ hat j+2 hat k\ a n d\ vecgamma= hat i+2 hat j+a hat k` are coplanar.`\ `

Explanation

$$
\begin{aligned}
{[\vec{a} \cdot(\vec{l} \times \vec{c})] } &=0 \\
&\left|\begin{array}{lll}1 & 2 & 1 \\
a & 1 & 2 \\
1 & 2 & a
\end{array}\right|
\end{aligned}
...