ANGLE SUM
TRIANGLE = 180°
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Sum of the Angles of a Triangle
A
B
C
60°
45°
75°
60°
45°
60° + 75° + 45° = 180°
∠A + ∠B + ∠C
all three angles
= 180°
always!
straight line
= 180°
1. Rule
Every triangle: ∠A + ∠B + ∠C = 180°
Whether small or big
2. Proof Idea
Draw a line through C parallel to the base
Alternate angles are equal → straight line
3. Example
Two angles: 50° and 70°
teesra = 180 − 120 = 60°
MATRIC MATHS · GEOMETRY · PUNJAB BOARDS
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