A. Let \[ S=\{(z_1,\ldots ,z_n)\in \mathbb {C}^n:z_1^2+\cdots +z_n^2=1\}. \] Prove that \(S\) is a smooth (real) submanifold of \(\mathbb {C}^n=\mathbb {R}^{2n}\), and find it’s dimension.
B. Prove that the orthogonal group \(O(n)\) is a smooth submanifold of the space of \(n\times n\) matrices \(M(n)=\mathbb {R}^{n^2}\), and find it’s dimension.