10.07.2015 Views

Plane Geometry - Bruce E. Shapiro

Plane Geometry - Bruce E. Shapiro

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Section 26Side-Side-SideTheorem 26.1 (Side-Side-Side (SSS)) If △ABC and △DEF are trianglessuch that AB = DE, BC = EF , and CA = F D then △ABC ∼ =△DEF .Proof. Given AB = DE, BC = EF and AC = F D for triangles △ABCand △DEF .Figure 26.1: Proof of SSS, case H = A.By the triangle construction theorem there is a point G on the oppositeside of ←→ AB from C such that △DEF ∼ = △ABG.Let H = CG ∩ ←→ AB, which exists by the plane separation postulate becauseC and G are on opposite sides of ←→ AB.There are five possible cases: (1) H = A, (2) H = B, (3) A ∗ H ∗ B, (4)H ∗ A ∗ B, and (5) A ∗ B ∗ H.121

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