a^4+b^4+c^4=2c^2(a^2+b^2) ===> (a^2+b^2)^2-2a^2b^2+c^4-2c^2(a^2+b^2)=0 由余弦定理得到：a^2+b^2-c^2=2abcosC 所以：a^2+b^2=c^2+2abcosC ===> (c^2+2abcosC)^2-2a^2b^2+c^4-2c^2(c^2+2abcosC)=0 ===> c^4+4abc^...