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Geometry 15 Online
OpenStudy (anonymous):

Prove that sum of diagonals of a convex pentagon is greater than the perimeter but less than double the perimeter

OpenStudy (kc_kennylau):

I'd use the triangles ABC, BCD, CDE, DEA and EAB.

OpenStudy (kc_kennylau):

AC>AB, BD>BC, ... Therefore AC+BD+... > AB+BC+...

OpenStudy (kc_kennylau):

But AC<AB+BC, BD<BC+CD, ... Therefore AC+BD+... < AB+BC+BC+CD+CD+DE+DE+EA+EA+AB = 2*perimeter

OpenStudy (anonymous):

thank u

OpenStudy (kc_kennylau):

No problem

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