
adjacent angles 
two angles that have a common vertex and one common side. 
altitude 
in geometry, the perpendicular distance from a vertex to its base or opposite surface. [1/4 definitions] 
apex 
the uppermost point; tip; summit; vertex. [1/2 definitions] 
sine 
of an angle whose vertex is the center of a circle, and one of whose sides is on the x axis, the positive or negative ratio of the ordinate of the arc cut by the angle's other side to the radius of the circle. [1/2 definitions] 
triangulation 
a system used by navigators and surveyors to calculate the distance between two points, or the relative position of points on a plane, in which each known point is made the vertex of a triangle and each triangle is given a base line of known length. [1/2 definitions] 

