The Student Room Group

So confused

How does log2 (little 2) x= +_3 give x=1/8 as a solution??
Reply 1
Original post by Idk131
How does log2 (little 2) x= +_3 give x=1/8 as a solution??


I though you couldn't have a negative log but the answer gives the -3 solution not the positive one?
Reply 2
Anyone? I am really stuck on this and am not sure how logs even work now tbh, is there another formula/rule that I should be made aware of? I though the solution would be x=9 not 1/8
(edited 1 year ago)
Logs are indices.

In base 2 logs, log8= 3, since 2^3=8
In base 10 logs, log100= 2, since 10^2=100

Try to remember either of those two facts as a starting point of comprehension.

Can you post an actual piccie of the question, since something may have been lost in translation, as it were.
Reply 4
Original post by Idk131
I though you couldn't have a negative log but the answer gives the -3 solution not the positive one?


A logarithm can be negative, but you can't take the log of a negative (at least, not at A level)
log2x=alog_2{x} = a means 2a=x2^a = x, so have a think about what log2x=3log_2{x} = -3 is telling you :smile:
Original post by Idk131
How does log2 (little 2) x= +_3 give x=1/8 as a solution??


2^-3=x

or 1/2^3=x

or 1/8=x

That's it.
Reply 6
Ah ok thank you so much guys!
eh, why are we ignoring the 2^3 = 8 solution?
Original post by toxicgamage56
eh, why are we ignoring the 2^3 = 8 solution?

The op hasn't posted the actual question. There may have been a detail in it which explained why?

Quick Reply

Latest