A regular polygon has all sides equal and all interior angles equal. The vertex is located at the center of the regular polygon. To measure the vertex of any angle in a polygon, select any line on the outside of the shape and draw a line from each end of the line to the center point of the polygon. Label the left point of the line A, and label the right point of the line C. The point where the lines meet in the center is the vertex of that angle and is labeled B.
Vertex is also used to indicate the high point of an arc, or a curve, on a graph. A parabola is a shape on a graph that is defined by a quadratic equation, such as ax² + bx + c = 0. The vertex of the parabola is found at the top, or the peak, of the curve. The peak is either pointing upward on the graph and is positive, or downward on the graph and is negative.
To measure an angle, you have to align a protractor with the vertex. Use a protractor to measure the angle by aligning the 90 degree point (the center mark) on the straight edge of the protractor with the vertex. Rotate the protractor so one side of the protractor is aligned with one line of the angle. The zero should be at the end of one side of the angle. The point where the other line intersects with the protractor is the degree of the angle.
In geometry, the vertex is the point where two edges meet on the shape. In three-dimensional geometry, the vertex is where three or more edges meet at the same point. A cube has eight corners. The vertices of cubes, rectangles and pyramids are found at the corners of the shape. Each corner is a vertex from which the degree of the angle can be measured.