Geometric Proof

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# Geometric Proof - PowerPoint PPT Presentation

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.

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Presentation Transcript

### 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

Prove that the sum of the angles in a triangle is 180°

Angles on a straight line

<CBA + <CBE + <EBG = 180º

<ACB = <CBE

Alternate Angles

SO <CBA + <ACB + <CAB = 180º

<CAB = <EBG

Corresponding Angles

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?