Find the value of .
and form a straight angle (180).
If two sides of a triangle are congruent, then the two angles
opposite to those sides are also congruent. In ,
since , then .
To find , subtract 's two other
angle measures from .
Therefore, is an equilateral triangle.
All sides of an equilateral triangle are the same length. Write an
equation to show that is the same length as cm, and
solve for the value of .