D is a point on the bisector of an outer angle of the triangle ABC, connecting dB and DC to prove AB + AC < DB + DC
DB+DC>AB+AC
It is proved that △ CAD ≌ had can be easily proved by taking a point h on the extension line of Ba, making ah = AC, connecting DH
So CD = DH
In △ BDH, DH + DB > Hb
And DH = CD, ah = AC
∴DB+DC>AB+AC
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