What you’ll learn
Calculate arc measures.
Key idea
A central angle equals its intercepted arc; an inscribed angle equals half its intercepted arc.
Degrees measure arcs, not their lengths; distinguish full-circle complement from the half-arc rule.
Worked example
Enter the exact value or ordered values in the format requested below.
Circle O has minor central angle AOB=170 degrees. C is on the complementary major arc. Find the major arc ACB in degrees.
- The minor arc AB equals the central angle 170.
- Major arc ACB=360-170=190 degrees.
Answer: 190
Quick Check
Evaluate a worked attempt at calculate arc measures, identify the first invalid step, and provide the correction.
Minor central angle AOB=100 degrees. Student Step 1 sets minor arc AB=100. Step 2 finds major arc AB by halving to 50 degrees. Locate the first invalid step and correct the major arc.