Math:
begin{gather} sum_{n=1}^infty frac{1}{n^2} = frac{pi^2}{6}. end{gather}
begin{gather}
begin{bmatrix} Phi_{11} & Phi_{12} \ Phi_{21} & Phi_{22} end{bmatrix}
=
frac{1}{det(X)}
begin{bmatrix}
X_{22} Y_{11} – X_{12} Y_{21} &
X_{22} Y_{12} – X_{12} Y_{22} \
X_{11} Y_{21} – X_{21} Y_{11} &
X_{11} Y_{22} – X_{21} Y_{12}
end{bmatrix}
end{gather}