问题
选择题
如果（9n）2=312，则n的值是（ ）
A．4
B．3
C．2
D．1
答案
∵（9n）2={[（3）2]n}2=34n
∴34n=312，
∴4n=12，
∴n=3．
故选B．
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如果（9n）2=312，则n的值是（ ）
A．4
B．3
C．2
D．1
∵（9n）2={[（3）2]n}2=34n
∴34n=312，
∴4n=12，
∴n=3．
故选B．
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