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已知a2-3a-1=0,求a6+120a-2=.

题目详情
已知a2-3a-1=0,求a6+120a-2=___.
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答案和解析
∵a2-3a-1=0,
∴a2=3a+1,
a6=(a23=(3a+1)2(3a+1)=(9a2+6a+1)(3a+1)=[9×(3a+1)+6a+1](3a+1)=(33a+10)(3a+1)=99a2+63a+10=99(3a+1)+63a+10=360a+109,
∵a2-3a=1,
120a-2=
120
a2
(a2-3a)=120-
360
a
=120-
360
a
×(a2-3a)=120-360a+1080,
∴a6+120a-2=360a+109+120-360a+1080=1309.