An altitude of a triangle is a line or segment that passes through a vertex of the triangle and is to the line containing the opposite side.

I think best word to insert in the blank is the term "bisecting".

An altitude of a triangle is a line or segment that passes through a vertex of the triangle and is bisecting to the line containing the opposite side.

"Bisect" means to divide into two equal parts which is true for the altitude of a triangle.

31/6= 19/6 19/6 *1/7=19/42