Exercise 3.5.20

(a) Special solutions $(-1,2,0,0)$ and $\left(-\frac{1}{4},0,-3,1\right)$ are perpendicular to the rows of $R$ (and rows of $\mathit{ER}$ ). (b) $A^{T}y=0$ has 1 independent solution = last row of $E^{-1}$. ( $E^{-1}A=R$ has a zero row, which is just the transpose of $A^{T}y=0$ ).