Q: Verify Pythagoras for orthogonal u = (1,1,0), v = (1,-1,0). Check triangle inequality for (1,0),(0,1). ⟨u,v⟩ = 1-1 = 0: orthogonal ✓! ‖u+v‖² = ‖(2,0,0)‖² = 4. ‖u‖²+‖v‖² = 2+2 = 4 ✓! Triangle: ‖(1,1)‖ = √2 ≤ 1+1 = 2 ✓! (Orthogonal: Pythagoras holds!)