Consider the triangle ABN:
AN + BN > AB _______________ (1)
Consider the triangle BCN:
BN + CN > BC _______________ (2)
Consider the triangle ACN:
AN + CN > AC _______________ (3)
Adding both sides of (1), (2) and (3) we have
AN + BN + BN + CN + CN + AN > AB + BC + AC
2(AN + BN + CN) > AB + BC + AC
AN + BN + CN > (AB + BC + AC)/2