Scientific Calculator finding Log base X of Y

catching_streams

Eg How do I find Log (base 4) of 5 on a scientific calculator??
Any help much appreciated.......

JimG

log 5 (base 4) = (ln 5)/(ln 4), where ln means log to the base e (which is on your calculator).

catching_streams

thanks jim.

D-Generate

woah it's not "log5/log4" to get Log5(base4).

Ln is Log to the base e(my fav number)
The Log button itself is log to the base 10, massive difference!

Pherekydes

D-Generate wrote:

woah it's not "log5/log4" to get Log5(base4).

Ln is Log to the base e(my fav number)
The Log button itself is log to the base 10, massive difference!

Jim didn't mention "log5/log4". He specifically put ln5/ln4.

However, "log5/log4" will give you exactly the same answer.

Log (4) =0.602059991327962
Log (5) =0.698970004336019

Log (5)/Log(4) =1.16096404744368

ln (4) = 1.38629436111989
ln(5) = 1.6094379124341

ln (5)/ln(4) = 1.16096404744368

4^1.16096404744368 = 5

JimG

I used ln only because it would certainly be on the calculator. Any other base, such as 10, would do. The general rule for change of base is log a(base b) =
(log a (base c))/(log b(base c))