(a^2+b^2)^2-4a^2b^2=0
a^4+2a^2b^2+b^4-4a^2b^2=0
a^4-2a^2b^2+b^4=0
(a^2-b^2)^2=0
a^2-b^2=0
(a+b)(a-b)=0
∵a+b>0
∴a-b=0
a=b,等腰三角形
(a^2+b^2)^2-4a^2b^2=0
a^4+2a^2b^2+b^4-4a^2b^2=0
a^4-2a^2b^2+b^4=0
(a^2-b^2)^2=0
a^2-b^2=0
(a+b)(a-b)=0
∵a+b>0
∴a-b=0
a=b,等腰三角形