已知a-1/a=3,求a^4+1/a^4的值
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已知a-1/a=3,求a^4+1/a^4的值
已知a-1/a=3,求a^4+1/a^4的值
已知a-1/a=3,求a^4+1/a^4的值
a-1/a=3
所以 (a-1/a)²=a²+1/a²-2=9
a²+1/a²=11;
(a²+1/a²)²=a^4+1/a^4+2=121
故 a^4+1/a^4=119.
a^4+1/a^4
=(a^2+1/a^2)^2-2
=[(a-1/a)^2+2]^2-2
=[3^2+2]^2-2
=11^2-2
=121-2
=119
a^4+1/a^4
=a^4+1/a^4-2+2
=(a²-1/a²)²+2
=(a+1/a)²(a-1/a)²+2
=9(a+1/a)²+2
=9a²+18+9/a²+2
=9a²-18+9/a²+38
=9(a-1/a)²+38
=9×9+38
=119
对a-1/a=3进行两次平方,每一次平方后都要常数移到等式的右边
因为a-1/a=3 ;两边同时平方可得:a²+1/a²=11
(a²+1/a²)×(a²+1/a²)=a^4+1/a^4+2=121
所以a^4+1/a^4=119