Question

已知10^a=25,10^b=1/4,求5a/5b的值

Answer 1

a=lg25 = lg (0.25 ×100) = lg (0.25) + lg 100 = lg (0.25) + 2,

b=lg(0.25)=lg(4^-1)= -1×lg4 = -1×2lg2 = -0.602,lg2=0.301这个你背住,应该当做已知的.

结果你就知道咯