As for the quad problem:

It's a tough one if the points make a random quad. But once you realise three points are in a straight line it becomes easier. So maybe that was deliberate?

Taking the two problems together it looks like the book is testing the triangle inequality in both so it begins to make sense.

Bob

]]>In any triangle with sides p, q and r

p + q > r

If you use this three times, taking a different side as r each time, then you will get inequalities involving n.

Also, the minus in the expression for AB leads to a fourth inequality.

All must be true so pick the most limiting which will give a lower bound.

Then you have the inequalities on the sides which will give an upper bound.

Bob

]]>theres a figure but im new so I cant post wahh

The sides are AB = 4n-9, BC = 3n+4, AC = 3n+1.

I figured out BC is the biggest and AC is second and AB is third biggest. pls help. thx a ton!!!!!:D