In the figure above, . What is the value of x ?
72
66
64
58
Choice C is correct. Since , it follows that
is an isosceles triangle with base RU. Therefore,
and
are the base angles of an isosceles triangle and are congruent. Let the measures of both
and
be
. According to the triangle sum theorem, the sum of the measures of the three angles of a triangle is
. Therefore,
, so
.
Note that is the same angle as
. Thus, the measure of
is
. According to the triangle exterior angle theorem, an external angle of a triangle is equal to the sum of the opposite interior angles. Therefore,
is equal to the sum of the measures of
and
; that is,
. Thus, the value of x is 64.
Choice B is incorrect. This is the measure of , but
is not congruent to
. Choices A and D are incorrect and may result from a calculation error.