a^4+b^4+c^4-2c^2(a^2+b^2)=0
(a^2+b^2-c^2)2=a^4+b^4+c^4-2c^2(a^2+b^2)+2a^2b^2
(a^2+b^2-c^2)2=2a^2b^2
cos(C)=(a^2+b^2-c^2)/2ab=±√2/2
角C等于45或135度
a^4+b^4+c^4-2c^2(a^2+b^2)=0
(a^2+b^2-c^2)2=a^4+b^4+c^4-2c^2(a^2+b^2)+2a^2b^2
(a^2+b^2-c^2)2=2a^2b^2
cos(C)=(a^2+b^2-c^2)/2ab=±√2/2
角C等于45或135度