Triangles
Grade 8 math lesson on triangles covering types, angle sum theorem, and triangle properties. Students learn to classify triangles by sides (equilateral, isosceles, scalene) and angles (acute, right, obtuse), and apply the rule that interior angles sum to 180 degrees.
Key Concepts
New Concept This course bridges arithmetic with algebra and geometry. You will master core skills and apply them to solve increasingly complex and interesting real world problems. What’s next This lesson begins our journey into geometry. We will start by classifying different types of triangles and then learn how to calculate their area.
Common Questions
What are the different types of triangles?
Triangles are classified by sides: equilateral (all sides equal), isosceles (two equal sides), scalene (no equal sides). By angles: acute (all angles less than 90), right (one 90-degree angle), obtuse (one angle greater than 90).
What is the triangle angle sum theorem?
The interior angles of any triangle always add up to 180 degrees. This means if you know two angles, you can find the third by subtracting their sum from 180.
What is an isosceles triangle?
An isosceles triangle has exactly two equal side lengths, called legs. The angles opposite the equal sides (base angles) are also equal. Isosceles triangles appear frequently in geometry proofs and real-world structures.
How do you find a missing angle in a triangle?
Add the two known angles together, then subtract from 180. For example, if two angles are 45 and 75 degrees, the third angle is 180 - 45 - 75 = 60 degrees.