若3^x=12,3^y=4,则9^x-y=
谢谢
人气：245 ℃ 时间：2020-06-26 08:30:51
解答
9^(x-y)
=(3^2)^(x-y)
=3^(2x-2y)
=3^2x÷3^2y
=(3^x)^2÷(3^y)^2
=12^2÷4^2
=144÷16
=9
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