题目有误,不是平方应该是四次方a^4+ b^4+c^4+d^4=4abcda^4+b^4+c^4+d^4-4abcd=0 a^4+b^4-2a^2b^2+c^4+d^4-2c^2d^2-4abcd+2a^2b^2+2c^2d^2=0 (a^2-b^2)^2+(c^2-d^2)^2+2(ab-cd)^2=0 则有a^2=b^2,c^2=d^2,ab=cd即a=b=c...