We know that,
#color(red)((1)1/(a^n)=a^(-n)#
#color(blue)((2)log_a x^n=nlog_a x#
#color(violet)((3)log_a a=1#
Let
#L=log_10(1/100)-log_10(1/1000)#
#=log_10color(red)((1/(10^2)))-log_10 color(red)((1/(10^3))...toApply(1))#
#=log_10(10^color(blue)((-2)))-log_10(10^color(blue)((-3)))...tocolor(blue)(Apply(2))#
#=color(blue)(-2)log_10 10-color(blue)((-3))log_10 10#
#=-2color(violet)((1))+3(color(violet)(1))...tocolor(violet)(Apply(3)#
#=-2+3#
#=1#