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问题: 已知a-1/a=3,求a^4-1/a^4的值

过程请详细

解答:

a-1/a=3,9=(a-1/a)^2=a^2-2+1/a^2,
a^2+1/a^2=11,
a^2+2+1/a^2=13=(a+1/a)^2
a^4-1/a^4=[a^2+(1/a^2)][a^2-(1/a^2)]
==[a^2+(1/a^2)][a-(1/a)][a+(1/a)]=3*11*根号(13)
=33*根号(13)