若2^a=3 4^b=9 求 2^5a-4b - 知识问答

若2^a=3 4^b=9 求 2^5a-4b

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a=㏒2 3 b=㏒4 9
2^5a-4b=2^(5log2 3-4log4 9)
=2^(log2 3^5-4*(1/2)log2 9)
=2^(log2 3^5-2*(1/2)log2 9^2)
=2^(log2 3^5-log2 9^2)
=2^log2 (3^5/9^2)
=3^5/9^2
=3

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