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若3^(y/2)=9,则3^(-y)=()A.81B.1/81C.3D.1/3〔(x^(-1)+y^(-1)〕^(-1)化去负指数后等于()A.x+yB.(x+y)/xyC.xy/(x+y)D.1/xy

题目详情
若3^(y/2)=9,则3^(-y)=()
A.81
B.1/81
C.3
D.1/3
〔(x^(-1)+y^(-1)〕^(-1)化去负指数后等于( )
A.x+y
B.(x+y)/xy
C.xy/(x+y)
D.1/xy
▼优质解答
答案和解析
B.1/81
C.xy/(x+y)