Recap

Determinant

$$\det (\left[\begin{array}{cc}a& b\\ c& d\end{array}\right])=ad-cb$$ $$\det (\left[\begin{array}{ccc}a& b& c\\ d& e& f\\ g& h& i\end{array}\right])=a(ei-fh)-b(di-fg)+c(dh-eg)$$

Eigenvalues

Notation: $\lambda$

solve $\det (A-\lambda I)=0$

Singular value

Notation: $\delta$

${\delta }^2=\lambda$

Inverse of martixs

$(AB{)}^T=B^T{A}^T$