Suppose $\hat{A}$ is the triangular matrix we obtained after the Householder transformation, $$\hat{A} = \hat{Q}\hat{U},$$ and multiply from the left with $\hat{Q}^{-1}$ resulting in $$\hat{Q}^{-1}\hat{A} = \hat{U}.$$ Suppose that $\hat{Q}$ consists of a series of planar Jacobi like rotations acting on sub blocks of $\hat{A}$ so that all elements below the diagonal are zeroed out $$\hat{Q}=\hat{R}_{12}\hat{R}_{23}\dots\hat{R}_{n-1,n}.$$