等边
a^4+b^4+c^4=a^2b^2+b^2c^2+a^2c^2
2（a^4+b^4+c^4）=2（a^2b^2+b^2c^2+a^2c^2）
a^4+b^4-2a^2b^2+a^4+c^4-2a^2c^2+b^4+c^4-2b^2c^2=0
(a^2-b^2)^2+(a^2-c^2)^2+(b^2-c^2)^2=0
a^2=b^2,a^2=c^2,b^2=c^2
a=b=c