Angles
A right angle measures 90 degrees and is usually indicated in a diagram by a little box. The figure above is a right angle. Lines that
intersect to form right angles are said to be perpendicular. Two adjacent angles that form a right angle are called complementary
angles.
RULE TO REMEMBER
A straight angle contains 180º.Angles that form a straight line add up to 180 degrees. In the figure above, a + b = 180.
When two lines intersect, adjacent angles are supplementary, meaning they add up to 180 degrees. In the figure above, a + b =
180.