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Geometric Proof. GCSE Higher. Prove that the sum of the angles in a triangle is 180°. We can use previous knowledge of the properties of parallel lines. C. EXTEND the line AB to a point G. E. DRAW line BE parallel to AC. A. B. G. C. E. A. B. G. - PowerPoint PPT Presentation
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Geometric Proof
GCSE Higher
Prove that the sum of the angles in a triangle is 180°
A
C
B
We can use previousknowledge of the properties ofparallel lines
EXTEND the line AB to a point G
G
DRAW line BE parallel to AC
E
Prove that the sum of the angles in a triangle is 180°
A
C
B G
E
<ACB = <CBE Alternate Angles
<CAB = <EBG Corresponding Angles
<CBA + <CBE + <EBG = 180º Angles on a straight line
SO <CBA + <ACB + <CAB = 180º
The Angle Sum of a triangle is 180º
Using this …
…could you prove that the exterior angle of a triangle is equal to the sum of the two opposite interior angles?
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