ALTITUDES / ORTHOCENTER
These are the ALTITUDES of a triangle.
Their point of concurrency is the ORTHOCENTER.
Drag around the vertices and sides of the triangle and notice what happens to the ALTITUDES and ORTHOCENTER. When is the ORTHOCENTER inside of the triangle? When is the ORTHOCENTER outside of the triangle?
Notice that the product of the distance {ORTHOCENTER to VERTEX } and {ORTHOCENTER to OPPOSITE SIDE} is the same for all three ALTITUDES. You do not "have to" know this, but it is pretty cool!