show that
ab+ac+bc=<a^2+b^2+c^2
i've done a similar example and trying to do what i did there with this one but just not working out. below is the one i've already done
2ab=<a^2+b^2
i did like this
since
(a-b)^2=a^-2ab+b^2
thus
a^2+b^2=(a-b)^2+2ab
but
(a-b)^2>=0
then
a^2+b^2>=2ab