But wait — reconsider: “invariant under \(90^\circ\) rotationâ€ means \( R\mathbf{v} = \mathbf{v} \), which we solved gives \( x = -y \) and \( x = y \Rightarrow x = 0, y = 0 \). So only trivial fixed vector.

Thu, 30 Apr 2026 14:09:29 +0000

Content under review