Let vectors P1, P2, and P3 be defined as follows:
P1 = [1 2 3 4] $^{T}$, P2 = [4 -2 -6 -7]$^{T}$, and P3 = [3 4 -2 1]$^{T}$
Let $x = [1 \, 2\, 3\, 7]^{T}$
This question is compromised into two parts:
a. Determine the closest vector $\hat{x}$ in span [P1, P2, P3].
b. Determine the orthogonal complement of x in span[P1, P2, P3].
Part a. is simply the projection x onto the subspace spanned by those vectors: $A(A^{T}A)^{-1}A^{T}x$. However, I am unsure about part b. I know that $x - \dot{x}$ is the orthogonal complement to the subspace spanned by [P1, P2, P3], but how do I find the orthogonal complement of x $\textbf{in}$ span [P1, P2, P3]?