Mrs.D Math · 6th Grade

TRIANGLE
TRIUMPH

Geometry · Types, Angles & Sides
🔹 Equilateral
🔹 Isosceles
🔸 Acute
🔸 Obtuse
🔹 Right
📏 3 + 4 > 5 ✓
📐 Angles = 180°
🔺 60° + 75° + ? = 180°
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📚 How It Works

Is It a Triangle? — The Side Length Rule

The sum of the lengths of any two sides of a triangle must be GREATER than the length of the third side. Shortcut: add the two shortest sides and compare to the longest.

✓
3 in, 4 in, 5 in: 3 + 4 = 7, and 7 > 5 → YES, it is a triangle!
3 + 4 > 5 ✓
✗
3 in, 4 in, 7 in: 3 + 4 = 7, but 7 is NOT greater than 7 → NO triangle.
3 + 4 = 7, not > 7 ✗
3
Types by sides: Equilateral = all 3 equal · Isosceles = 2 equal · Scalene = none equal. Types by angles: Acute (all < 90°) · Right (one = 90°) · Obtuse (one > 90°).

Finding a Missing Angle

The sum of the measures of the angles in a triangle is 180°. Set up an equation and solve!

1
Angles 60° and 75°: 60 + 75 + x = 180 → 135 + x = 180 → x = 45°
180 − 135 = 45
2
Isosceles triangles have 2 equal base angles. If the vertex angle is 100°: 180 − 100 = 80, then 80 ÷ 2 = 40° each.

How to Play

🔺
Triangle Types — Decide if side lengths can form a triangle, or name the triangle type. Choose from 4 answers.
📐
Missing Angle — Study the triangle diagram and type the missing angle measure in degrees.
🌀
Mixed — Both types together for the ultimate challenge!
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TRIANGLE TYPES
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