I'm having trouble with the right side of this problem: 10^-x = 5^4x. Why is 10^-x = 5^4x processed to -x log 10 = 4x log 5? The right side means 4x log (base 10) 5, right? I'm confused because the 5 on the right side of the original problem is that side's base. Why wouldn't it be: -x log 10 = 4x log base 5? Seems like in some problems the number in that spot, ie the 5, is used as the log base and sometimes it isn't, and I don't know when or why. Please help, as the final's in 1.5 days!