Altitude of a triangle
= Altitude of a triangle
= Triangle altitude
{synonym}
An altitude of a <triangle> is the whole <line> through one vertex that is <orthogonal> to the <line> through the opposite side. For vertex $A$ and opposite vertices $B,C$, its <equation> in <position vectors> is $(\mathbf x-\mathbf a)\cdot(\mathbf c-\mathbf b)=0$. The three such <lines> meet at the <orthocenter>; they need not meet inside the <triangle>.