若3^a=8,3^b=5,则3^(a/3-2b)=?
问题描述:
若3^a=8,3^b=5,则3^(a/3-2b)=?
8^a=1/4,求a=?
答
3^a=2^3
a=3log3(2)
b=log3(5)
a/3-2b=log3(2)-2log3(5)=log3(2)-log3(25)=log3(2/25)
a=log8(1/4)=log2^3(2^-2)=-2/3