Hey I've got two questions (no answers so ones more of just double checking some working!)

Firstly can someone have a look over this for me:

my reasoning is this

if we change the parameter now by letting

we then have

so this would be a circle of radius

centered on c

as

(does this get around the problem that

can be negative?)

or did I screw up somewhere!

and for the second question any chance of a little hint because I cant see where to start with this

for this ive worked out that the final condition implys that if each of the numbers a,b,c were written as

etc.

then

but I cant see a way to apply it so any chance of a hint

many thanks

Simon