Classifying 2D Shapes — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
A hexagon has five sides and five angles.
Corrected: A hexagon has six sides and six angles.
The prefix "hex" means six, so a hexagon always has six sides and six angles, not five.
2. Fix the sentence:
A regular polygon has sides of different lengths.
Corrected: A regular polygon has all sides equal in length and all angles equal in measure.
The word "regular" means all sides are equal in length and all angles are equal in measure, so having sides of different lengths would make it irregular.
3. Fix the sentence:
An octagon has ten sides and ten angles.
Corrected: An octagon has eight sides and eight angles.
The prefix "oct" means eight (like an octopus has eight arms), so an octagon has eight sides and eight angles, not ten.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. A polygon with seven sides is called a heptagon.
The prefix "hept" means seven, so a seven-sided polygon is called a heptagon.
2. The sum of interior angles in a triangle is 180° and in a quadrilateral is 360 degrees.
A quadrilateral can be split into two triangles, and since each triangle has 180°, the sum of interior angles is 2 x 180° = 360°.
3. A closed plane figure made of straight line segments is called a polygon.
A polygon is defined as a closed, flat shape made entirely of straight line segments — circles and curves do not qualify.
4. A regular hexagon has 6 equal interior angles.
A hexagon has six angles, and when it is regular, all six of those interior angles are equal, each measuring 120°.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. What is the difference between a regular polygon and an irregular polygon? Give one example of each.
Sample answer: A regular polygon has all sides and all angles equal, like a regular pentagon. An irregular polygon has sides or angles that are not all equal, like a rectangle.
A good answer includes: A regular polygon has all sides and all angles equal, like a regular pentagon. An irregular polygon has sides or angles that are not all equal, like a rectangle.
2. How can you find the sum of interior angles of any polygon if you know the number of sides?
Sample answer: You subtract 2 from the number of sides and multiply by 180°. For example, a pentagon has (5 − 2) × 180° = 540°.
A good answer includes: You subtract 2 from the number of sides and multiply by 180°. For example, a pentagon has (5 − 2) × 180° = 540°.