step-by-step
\begin{pmatrix}\frac{1}{\sqrt{6}} & -\frac{1}{\sqrt{2}} & \frac{1}{\sqrt{3}}\\ \frac{1}{\sqrt{6}} & \frac{1}{\sqrt{2}}& \frac{1}{\sqrt{3}}\\ -\frac{2}{\sqrt{6}} & 0 & \frac{1}{\sqrt{3}}\end{pmatrix}\begin{pmatrix}7& 0& 0 \\ 0 & 1& 0\\ 0 & 0 & 1\end{pmatrix}\begin{pmatrix}\frac{1}{\sqrt{6}} & -\frac{1}{\sqrt{2}} & \frac{1}{\sqrt{3}}\\ \frac{1}{\sqrt{6}} & \frac{1}{\sqrt{2}}& \frac{1}{\sqrt{3}}\\ -\frac{2}{\sqrt{6}} & 0 & \frac{1}{\sqrt{3}}\end{pmatrix}^{T}
en