Exterior Angle Theorem of Triangles — Practice Geometry Questions
In geometry, you can use the exterior angle of a triangle to find a missing interior angle. The following practice questions ask you to do just that, and then to apply some algebra, along with the properties of an exterior angle, to find a missing variable.
Practice questions
Use the figure and the given information to answer the following questions.

In triangle WXY,

In triangle WXY,
Each angle is represented by the following:
Solve for the variable b.
Answers and explanations

70 degrees
The exterior angle of a triangle is equal to the sum of the two nonadjacent interior angles of the triangle, so set up an equation and solve for x:
Plug in the value for x to find

120 degrees
The exterior angle of a triangle is equal to the sum of the two nonadjacent interior angles of the triangle. Use this relationship to solve for a:
Plug in the value of a to find
The angles of a triangle add up to 180 degrees. Therefore,