simplify (xa/xb)a+b* (xb/xc)b+c* (xc/xa)c+a
(xa / xb)a+b * (xb/xc)b+c * (xc /xa) c+a
= (xa-b)a+b * (xb-c)b+c * (xc-a)c+a
= xa2 - b2 * xb2 -c2 * xc2 -a2
= xa2 -a2 +b2-b2 +c2-c2
= x0
= 1
= (xa-b)a+b * (xb-c)b+c * (xc-a)c+a
= xa2 - b2 * xb2 -c2 * xc2 -a2
= xa2 -a2 +b2-b2 +c2-c2
= x0
= 1