a²-16b²-c²+6ab+10bc=0
a²+9b²-25b²-c²+6ab+10bc=0
a²+9b²+6ab-25b²-c²+10bc=0
(a²+9b²+6ab)-(25b²+c²-10bc)=0
(a+3b)²-(5b-c)²=0
(a+3b+5b-c)·(a+3b-5b+c)=0
(a+8b-c)·(a-2b+c)=0
a+8b=a+b>c,所以a+8b-c>0
所以a-2b+c=0,即a+c=2b