Find the complement of 28°.
Incorrect answer: 152°
Adjacent angles are not automatically supplementary; their outside sides must form a straight line. Vertical angles are opposite at an intersection, not side by side.
Mixing up complementary and supplementary angles
Complements sum to 90 degrees; supplements sum to 180 degrees. Choose the total before subtracting.
The correction
62°
90 − 28 = 62.
- Use stated facts or markings to identify a right angle, straight line, or intersection.
- Translate the relationship into a sum or equality.
- Solve and check that the measures are sensible; do not rely on a diagram looking accurate.
Try the reasoning in another example
A linear pair contains angles of 112° and x°. Find x.
- A straight angle is 180°, so x + 112 = 180.
- Subtract 112.
Answer: 68°
Explain why each step preserves the quantity or relationship. If you can compute the answer but cannot explain the step, revisit the model before adding more questions.
The short check below reuses the first example as a retrieval question and adds a second question. It checks this method; it does not establish a grade level.
Your next step
2 questions · No time limitCheck this step for yourself
Choose an answer or enter it as shown. You can include units. Select “Not sure yet” to mark a skill for practice. Results stay on this page unless you download them.