Angles and Measurement — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
Two angles that add up to 180° are called complementary angles.
Corrected: Two angles that add up to 180° are called supplementary angles.
The corrected sentence is: "Two angles that add up to 180° are called supplementary angles." The error was confused complementary and supplementary: the original sentence "Two angles that add up to 180° are called complementary angles." needed to be fixed.
2. Fix the sentence:
The supplement of a 60° angle is 30° because 60 minus 30 equals 30.
Corrected: The supplement of a 60° angle is 120° because 180° minus 60° equals 120°.
The corrected sentence is: "The supplement of a 60° angle is 120° because 180° minus 60° equals 120°." The error was wrong supplementary calculation: the original sentence "The supplement of a 60° angle is 30° because 60 minus 30 equals 30." needed to be fixed.
3. Fix the sentence:
A 150° angle is acute because it is a large number.
Corrected: A 150° angle is obtuse because it is greater than 90° but less than 180°.
The corrected sentence is: "A 150° angle is obtuse because it is greater than 90° but less than 180°." The error was wrong angle classification: the original sentence "A 150° angle is acute because it is a large number." needed to be fixed.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. Two angles that add up to 180° are called supplementary angles.
Supplementary angles always add up to 180°, so when two angles combine to make a straight line, they are called supplementary.
2. The complement of a 50° angle is 40 degrees.
Complementary angles add up to 90°, so subtract 50° from 90° to get 40°.
3. The supplement of a 135° angle is 45 degrees.
Supplementary angles add up to 180°, so subtract 135° from 180° to get 45°.
4. An angle between 0° and 90° is always acute.
Any angle measuring less than 90° is classified as acute, so every angle between 0° and 90° falls in that category.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. What is the difference between complementary and supplementary angles?
Sample answer: Complementary angles add up to 90°, while supplementary angles add up to 180°.
A good answer includes: Complementary angles add up to 90°, while supplementary angles add up to 180°.
2. If two angles are supplementary and one is 70°, explain how to find the other angle.
Sample answer: Subtract 70° from 180° to get 110°. Since supplementary angles add up to 180°, the other angle must be 110°.
A good answer includes: Subtract 70° from 180° to get 110°. Since supplementary angles add up to 180°, the other angle must be 110°.