1 of 4

4.G.A.1

I CAN

compare an angle to a right angle and classify angles as acute, right, or obtuse.

NAME:

GEOMETRY

— TARGET 9 —

ACUTE, RIGHT, AND OBTUSE ANGLES

1

Is this angle smaller or larger than a right angle? (LEVEL 1)

2

Which of these is exactly a right angle? (LEVEL 1)

A. The acute angle

B. The obtuse angle

C. The angle with the square corner mark

D. The straight line

3

Classify each angle as acute, right, or obtuse. (LEVEL 2)

PART A

PART B

PART C

POST-ASSESSMENT

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Page 2

4

This figure has 4 angles. How many of those angles are acute? (LEVEL 3)

5

A student labeled every angle in this triangle "acute," but one is clearly wider than a square corner. (LEVEL 3)

PART A

Find and fix the error by naming the correct type for the widest angle

PART B

Can a triangle ever have two right angles? Explain using what you know about angle sizes

6

Create a 4-sided figure containing exactly two acute angles, one right angle, and one obtuse angle (LEVEL 4)

PART A

Draw the figure.

PART B

Explain how you know your figure meets all the conditions (you can mention using a paper corner to check)

I FEEL

1

2

3

4

POST-ASSESSMENT

3 of 4

4.G.A.1

I CAN

compare an angle to a right angle and classify angles as acute, right, or obtuse.

ANSWER KEY

NAME:

GEOMETRY

— TARGET 9 —

ACUTE, RIGHT, AND OBTUSE ANGLES

1

Is this angle smaller or larger than a right angle? (LEVEL 1)

ANSWER

Smaller (acute)

If a student says larger, they may be misreading the opening or comparing the lengths of the rays instead.

2

Which of these is exactly a right angle? (LEVEL 1)

A. The acute angle

B. The obtuse angle

C. The angle with the square corner mark

D. The straight line

ANSWER

C. The angle with the square corner mark

If a student picks the obtuse angle by eye, it means they aren't looking for or using the square-corner cue.

3

Angle (LEVEL 2)

PART A

Classify each angle as acute, right, or obtuse.

ANSWER

acute; Angle

Confusing acute and obtuse, or missing the right-angle mark, shows a need for vocabulary reinforcement.

PART B

ANSWER

right; Angle

PART C

ANSWER

obtuse

POST-ASSESSMENT

4 of 4

Page 2

4

This figure has 4 angles. How many of those angles are acute? (LEVEL 3)

ANSWER

2 acute angles

Miscounting often happens if a student classifies angles by the length of their rays, or if they miscount the wide/reflex angle.

5

A student labeled every angle in this triangle "acute," but one is clearly wider than a square corner. (LEVEL 3)

PART A

Find and fix the error by naming the correct type for the widest angle

ANSWER

The widest angle is obtuse, not acute

Agreeing that all are acute shows the student doesn't check against a right angle. Saying "yes" to 5B means they aren't reasoning about the total angles needed to close a shape.

PART B

Can a triangle ever have two right angles? Explain using what you know about angle sizes

ANSWER

No, two right angles (square corners) use up too much turning (180°), so the shape would never close to form a triangle

6

Create a 4-sided figure containing exactly two acute angles, one right angle, and one obtuse angle (LEVEL 4)

PART A

Draw the figure.

ANSWER

A quadrilateral with exactly the four requested angle types

Including an extra angle type or labeling completely by eye without a geometric check (like a paper corner) shows they haven't verified the constraints.

PART B

Explain how you know your figure meets all the conditions (you can mention using a paper corner to check)

ANSWER

Explanation verifying each angle against a 90° right angle (or paper corner)

I FEEL

1

2

3

4

POST-ASSESSMENT