你只雖然記住matrix multiplication個dimension change係m by r times r by n gives m by n，所以你會知道以上嘅products個dimensions會分別係1 by 1, 4 by 4, 1 by 1, not existing，即係i同iii啱

有啲似information science

3&4，vector係括號打橫寫，方括打直寫，2支都係4x1 matrix (row x col, 考試唔記得就畫個十字叫神打救你😂） transpose左就係1x4 i) 4x4 ii) 1x1 iii) 4x4 iv) 4x1 (xTy 1x1變scalar)