What you’ll learn
Solve parallel-line/transversal angle problems.
Key idea
Corresponding and alternate-interior pairs are equal; same-side interior pairs are supplementary, not generally equal.
Named equal pairs differ from same-side supplementary pairs; the angle value and expression variable are separate quantities.
Worked example
Enter the exact value or ordered values in the format requested below.
Two parallel lines are crossed by a transversal. Angle x corresponds to a labeled 100-degree angle. Enter numerical x in degrees.
- For parallel lines, corresponding and alternate-interior angles equal the given 100 degrees.
- The named equal-angle pair therefore has unknown angle 100 degrees; supplement 80 would apply to a different, same-side pair.
Answer: 100
Quick Check
Evaluate a worked attempt at solve parallel-line/transversal angle problems, identify the first invalid step, and provide the correction.
Find an alternate-interior angle to 80 degrees on parallel lines. Step 1 identifies the pair as alternate interior. Step 2 uses 180-80=100. Locate the first invalid step and correct it.