21.当n为自然数时,有x^6n+1/x^6n=2 ..21.当n为自然数时,有x^6n+1/x^6n=2 证明:(1)x+1/x=-1 ==>x^6n+1/x^6n=2 (2)x+1/x=1 ==>x^6n+1/x^6n=2 22.证明:(1)a^2+b^2+c^2+d^2-ab-bc-cd-da=0 ==>a=b=c=d (2)a^4+b^4+c^4+d^4-4abcd=0 ==>a=b=c=d

问题描述:

21.当n为自然数时,有x^6n+1/x^6n=2 ..
21.当n为自然数时,有x^6n+1/x^6n=2
证明:(1)x+1/x=-1 ==>x^6n+1/x^6n=2
(2)x+1/x=1 ==>x^6n+1/x^6n=2
22.证明:(1)a^2+b^2+c^2+d^2-ab-bc-cd-da=0 ==>a=b=c=d
(2)a^4+b^4+c^4+d^4-4abcd=0 ==>a=b=c=d