Classifying Triangles — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
A yield sign in Grade 4 has all sides different, so it is a scalene triangle.
Corrected: A yield sign has all three sides congruent, so it is an equilateral triangle.
Yield signs are designed as equilateral triangles, with three congruent sides and three equal angles.
2. Fix the sentence:
A thin slice of pizza with two long equal sides is a equilateral triangle.
Corrected: A thin slice of pizza with two long equal sides is an isosceles triangle.
When a triangle has only two equal sides, like a pizza slice, it is classified as isosceles, not equilateral.
3. Fix the sentence:
A kite shape with three sides of different lengths is classified as a isosceles triangle.
Corrected: A kite shape with three sides of different lengths is classified as a scalene triangle.
If every side has a different length, the triangle is scalene because no sides are congruent.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. A traffic yield sign has three congruent sides, so it is an equilateral triangle.
An equilateral triangle has all three sides congruent and all three angles equal to 60 degrees.
2. A pizza slice with two equal long sides and one shorter side is an isosceles triangle.
Isosceles triangles have exactly two congruent sides meeting at a vertex called the apex.
3. A triangle with sides 5 cm, 7 cm, and 9 cm is called a scalene triangle.
When no sides of a triangle are congruent, we classify it as scalene.
4. Each angle inside an equilateral triangle measures 60 degrees.
Since all three angles in an equilateral triangle are congruent and sum to 180, each one measures 60 degrees.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Look around your classroom for a triangle. Name the object and classify the triangle by its sides.
Sample answer: A music stand bracket forms a triangle with three sides that look the same length, so I would classify it as an equilateral triangle.
Classifying by sides means deciding if a triangle is equilateral, isosceles, or scalene based on which sides are congruent.
2. Why is a yield sign classified as an equilateral triangle and not a scalene triangle?
Sample answer: A yield sign is equilateral because all three of its sides are congruent. A scalene triangle would have three sides of different lengths.
Equilateral and scalene are opposites: equilateral has all sides the same, while scalene has all sides different.