Question

please prove the 1st part only

Answer 1

Let us assume that the there is a quadrilateral ABCD, one of its diagonal be AC

This impies that AB + BC > AC - 1

AC + CD > DA this implies that AC > DA - CD -2

from 1 and 2

AB + BC > AC > DA - CD

THIS IMPLIES THAT AB + BC > DA - CD

THIS IMPLIES THAT AB + BC + CD > DA

HENCE PROVED

Answer 2

Answer:

do as what given in the first answer