Pairs of Angles

	Adjacent angles are angles in the same plane that have a common vertex and a common side but no common interior points. For example, angle HKF and angle FKI are adjacent angles. Can you find some more pairs of adjacent angles in the diagram? How many adjacent angles are in the following picture?
	Vertical angles (or opposite angles) are two nonadjacent angles formed by intersecting lines. Their sides form two lines (EF & GH); the vertical angles are the ones opposite each other (EKG & HKF). Notice that the angles have only one point in common, the vertex (K). How many pairs of vertical angles are in this diagram? What is the relationship between the angles opposite each other?
	Congruent angles are the same size; they have exactly the same measure. Perhaps you noticed that all vertical angles are also congruent angles.
	Complementary angles are two angles whose sum is 90. Notice that at all times angle BAT + angle CAT = 90.The diagram to the left is the typical representation of complementary angle but the angles do not have to be adjacent as shown here to be complementary.
	Supplementary angles are two angles whose sum in 180. Notice that at all times angle ABG + angle CBG = 180If they are the angles are adjacent (as in this diagram) they may be called a linear pair because they form a straight line.

Return to Points, Lines & Angles