A right angle is an angle equal to half the angle from one end of a line segment to the other. A right angle is 
radians or 
. A triangle containing
a right angle is called a right triangle. However,
a triangle cannot contain more than one right angle,
since the sum of the two right angles plus the third angle would exceed the 
total possessed by a triangle.
The patterns of cracks observed in mud that has been dried by the sun form curves that often intersect in right angles (Williams 1979, p. 45; Steinhaus 1999, p. 88; Pearce 1990, p. 12).
