When two parallel lines are intersected by a third line (called a transversal), congruent pairs of angles are formed, including alternate interior angles and alternate exterior angles.
The following practice questions ask you to use this information to find a missing angle, and then to apply some algebra to calculate a missing variable.
Practice questions
Use the diagram and the given information to solve the problem.
Parallel lines
are cut by a transversal. If
is represented by
is represented by 4x – 45, find the value of x.
Parallel lines
are cut by a transversal. If
are represented by
respectively, find the degree measure of
Answers and explanations
20
are alternate interior angles. Alternate interior angles are congruent, so set their measures equal to each other and solve for x:
140 degrees
are alternate exterior angles. Alternate exterior angles are congruent, so set their measures equal to each other and solve for x:
which means they add up to 180 degrees. Use this info to solve for
