I cant figure out how to do log base formula - Casio Prizm FX-CG10 Color Graphing Calculator Black

Use the formula
log in base b of (a) =log_b(a)=log(a)/log(b)=ln(a)/ln(b)

Pressing 2 0 0 LN = will give you the natural logarithm of 200. If you need the common (base 10) logarithm, divide the result by the log of 10.

( 2 0 0 LN ) / ( 1 0 LN ) =
will give you the common log of 200.

Your calculator knows only the decimal logarithms log or log_10 and the natural logarithms (ln or log in base e).
So you cannot compute directly the logarithms in any bases other than 10 and e.
A workaround consists in using the relation
log in base b of a number a (log_b (a))
log_b(a)= (log_10(a) ) / (log_10 (b))
or the relation
log_b(a)= ln(a)/ln(b)

log_2(0.3)=log(0.3)/log(2) where log is log in base 10
Similarly
log_2(0.3)=ln(0.3)/ln(2)
As to the multiplicative factor you had at the beginning of your expression, just multiply the value obtained by one on the formulas above (both formulas will give the same result) by 0.3

The TI-83+ has keys for natural and common logarithms (base e and 10, LN and LOG, respectively). If you want to calculate the logarithm to another base, you have to use the relationship

LOGb(x) = LOG(x)/LOG(b) = LN(x)/LN(b)

You cannot. You must use the formula
log in base b of a =log(a)/log(b) or
log_b(a)=ln(a)/ln(b)
where log(a) is common logarithm of a and ln(a)= natural logarithm of a

If you had the TI84PLUS or TI84PLUS SE, you could have installed the newest OS upgrade and that upgrade uses math print which allows the user to calculate logarithms in any base directly.

Hi,
Your calculator cannot compute directly the logarithms in an arbitrary base, but you have the means to obtain that indirectly.
You can use either of the conversion formulas shown on the screen capture (on the right). On screen capture ln stands for natural logarithm.

If you want binary logarithms (logs in base 2) you use the relation
log_2 (x) =ln(x)/ln(2)
or
log_2(x)=log(x)/log(2)

Use whichever formula is shorter to key in (without pressing the 2nd key).

Hope it helps.

Hello,
Sorry I clicked the post a clarification request too fast.

You cannot compute it directly. You have to use the formula

log_18(number) = ln(number)/ln(18).

Here log_18 is log in base 18, ln is the natural logarithm (naeperian or log in base e).

Alternatively, you can use

log_18(number) = log(number)/log(18)

where log is log in base 10.

If you use those types of calculations a lot, it might be a good idea to get a Casio FX-115ES, or a Casio FX-991 ES. They have other nice features like fraction calculations and radicals.

Hope it helps.

Hello,
There is something missing in the formulation.

Any way you cannot calculate it directly on this calculator.You need to use the formula

log_5 (a)= ln(a) x log_5 (e) a is a positive integer

where log_5 means log in base 5 (my notation for the function)
e is the base of the natural logarithms (e=2.71928 )
ln is the natural log function

To obtain a more accurate value of e, calculate e^(1)
Here are some values of log(e) in different bases (for you to play with)

log_2(e)= 1.442695041
log_3(e)=0.9102392266
log_4(e)=0.7213475204
log_5(e)=0.6213349346
log_6(e)=0.5581106266
log_7(e)=0.5138983424
log_8(e)=0.4808983470
log_9(e)=0.4551196133
log_10(e)=log(e)=0.4342944819

If you have to use log in bases other than 10 or e, you will need a claculator that does that at the touch of a button. Some calculators that handle these calculations are the Casio FX-300ES, FX-115ES,FX-991ES, those called Natural Display, or WriteView(Sharp) or Textbook display.

Hope it helps.

It's simple here some logs:

log x base y = log x / log y
log (x*y) = log x + log y
log (x/y) = log x - log y
you just need to know that the default base of log in calculators is 10, so log x mean
log x base 10 = log x / log 10,
so write log x / log y for log x base y example:
log 8 base 2 = log 8 / log 2 that is how you write it on calculator, hope it was helpful

Please be more clear with the question.. Do you want me to analyze the formula?