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Triangle Angle Sum Theorem
Interior angles of any triangle always sum to 180°
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Angle A 60°
Angle B 70°
Angle C auto-calculated = 180° − A − B 50°
Angle Sum
A
60°
+
B
70°
+
C
50°
=
180°
✓ Always true for any triangle
The Proof
Step 1: Draw any triangle. Label the three interior angles A, B, C.
Step 2: Tear off (cut out) each of the three angle corners.
Step 3: Place the three angle pieces side by side, vertices touching a straight line.
Result: The three angles form a perfectly straight line = 180°.
Key Rule
For any triangle — no matter how big, small, or what shape — the three interior angles always add up to exactly 180°. This is true for acute, right, and obtuse triangles.