若10^2y=25,则a10^-y等于A5/1B1/625C-1/5或1/5D1/25已知7^m=3,7^n=5,则7^2m-n=

Question

若10^2y=25,则a10^-y等于
A 5/1
B 1/625
C -1/5或1/5
D 1/25
已知7^m=3,7^n=5,则7^2m-n=____

Answer 1

C,