Definition: Vertical angles are the angles that are vertically opposite to each other when two lines intersect.
Vertical Angles Theorem: Vertical angles are congruent to each other.
Triangle Angle-Sum Theorem: The sum of the measures of the interior angles of a triangle is 180°.
The diagram shows triangle with to given angles. By the Triangle Angle-Sum Theorem you can find the measure of third angle. Angles x and y are vertical, then they are congruent.
Answer Part A: option A
By the Triangle Angle-Sum Theorem, x°+30°+70°=180°,
x°=80°
and
x°=y°=80°.
Answer part B: option B
