Triangle Altitudes

The the altitudes of a triangle are the lines drawn from the
vertices perpendicular to the opposite sides. The lines $h_{A}$, $h_{B}$ and $h_{C}$ are the
respective altitudes from $A$, $B$ abd $C$. Pairwise, they intersect in 3 points.
The theorem says these three points coincide as the red point $J$

Patrick D. F. Ion, Created with GeoGebra