This Grade 4 worksheet introduces classifying triangles by angle. Students review right, acute, and obtuse triangles using sentence corrections, fill-in-the-blank questions, and short answer prompts. Hints connect 90 degree angles to the corner of a book, helping students see angles in everyday objects while building solid math vocabulary. This Grade 4 worksheet supports classroom practice and homework review at home.
Style:
Classifying Triangles
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
A triangle with one 90 degree angle is called an acute triangle.
Rewrite: A triangle with one 90 degree angle is called a right triangle.
2. Fix the sentence:
If all three angles in a triangle are less than 90 degrees, the triangle is obtuse.
Rewrite: If all three angles in a triangle are less than 90 degrees, the triangle is acute.
3. Fix the sentence:
A triangle that has one angle measuring 120 degrees is a right triangle.
Rewrite: A triangle that has one angle measuring 120 degrees is an obtuse triangle.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. A triangle with exactly one 90 degree angle is called a right triangle.
2. A triangle in which every angle measures less than 90 degrees is called an acute triangle.
3. A triangle with one angle that is greater than 90 degrees is called an obtuse triangle.
4. The point where two sides of a triangle meet is called a vertex.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Explain how to decide if a triangle is acute, right, or obtuse.
Look at the three angles of the triangle. If every angle is less than 90 degrees, it is acute. If one angle is exactly 90 degrees, it is right. If one angle is greater than 90 degrees, it is obtuse.
2. Why can a triangle have only one right angle or only one obtuse angle?
All three angles in a triangle add up to 180 degrees. If two angles were 90 degrees or more, they alone would equal at least 180 degrees, leaving nothing for the third angle.
Classifying Triangles
★ Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1) Fix the sentence:
A triangle with one 90 degree angle is called an acute triangle.
Rewrite: A triangle with one 90 degree angle is called a right triangle.
2) Fix the sentence:
If all three angles in a triangle are less than 90 degrees, the triangle is obtuse.
Rewrite: If all three angles in a triangle are less than 90 degrees, the triangle is acute.
3) Fix the sentence:
A triangle that has one angle measuring 120 degrees is a right triangle.
Rewrite: A triangle that has one angle measuring 120 degrees is an obtuse triangle.
★ Part B: Fill in the Blank
Write the missing word or number on each line.
1) A triangle with exactly one 90 degree angle is called a right triangle.
2) A triangle in which every angle measures less than 90 degrees is called an acute triangle.
3) A triangle with one angle that is greater than 90 degrees is called an obtuse triangle.
4) The point where two sides of a triangle meet is called a vertex.
★ Part C: Short Answer
Answer each question in one or two complete sentences.
1) Explain how to decide if a triangle is acute, right, or obtuse.
Look at the three angles of the triangle. If every angle is less than 90 degrees, it is acute. If one angle is exactly 90 degrees, it is right. If one angle is greater than 90 degrees, it is obtuse.
2) Why can a triangle have only one right angle or only one obtuse angle?
All three angles in a triangle add up to 180 degrees. If two angles were 90 degrees or more, they alone would equal at least 180 degrees, leaving nothing for the third angle.
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9 Questions
15-20 minutes
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