#1
I just started with logarithms, and I'm pretty clueless about them. So here's one of the questions I have, and if you can explain it, I'll probably be able to figure out the rest.

NB: all the bases for these questions are x

If log 3 = 1.5, log 5 = 1.8 and log 10 = 3.0 :

evaluate log 15


thanks in advance
#2
which base are you using
Hi

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#3
in the book, the base just says x

edit: ya liek I said I'm pretty much clueless about all this
#4
log 15 should be log 3 times 5
Edit: but ive got no idea im going off logic
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#5
cant exactly remember but i think when you multiply logs you add wat their value is together

so log3 x log 5 = 1.5 + 1.8

not exactly sure tell me if its wrong ill actually get the book out
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#6
the answer for that Q is meant to be 3.3, but I don't know how to get it

edit: and ur answer is correct, cheers
#7
if log_a b = c
then a^c = b

log_x 3 = 1.5
x^1.5 = 3
x =3^(1/1.5) =3^(2/3)

and so on for the others

if you need to work out what the base is
#8
log15 = log(3x5) = log3 +log5

One rule of logarithms is:
log(ab) = loga +logb
The handiness of this is that what was a multiplication problem has become an addition problem.

A few others:
log(a/b) = loga - logb
log(a^r) = r x loga
That's probably all you need.
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