How do i use log functions on the HP 39g+. For instance i want to use log10 1000 which should equal 3 or 3^5=243 so log3 243 should equal 5. If i press log the calculator shows: log( If i write log(3) then add 243 to show log(3)243 the answer is 115.940 NOT 243 5 like it should be. Please help.

easy:
2log(x) + log(3/4) - log(2x + 3/4) = 0
log(x^2) + log(3/4) = log(2x + 3/4)
log(3/4*x^2) = log(2x + 3/4)
3/4*x^2 = 2x + 3/4
multiply equation by 4:
3x^2 = 8x + 3
3x^2 - 8x - 3 = 0
solve this quadratic eq. and you get
x1 = 3
x2 = -1/3

does it make sense?

Most calculators can't do logs in different bases, but you can solve for the answer this way:

Let's say you need to take the log of 5 in base 3. This can also be written as log5 (base 10)/log3 (base 10).

A more technical solution can be found here: http://oakroadsystems.com/math/loglaws.htm#NewBase

The 30XA only has logarithm functions for base e and base 10. However, you can calculate the logarithm to any base by using the relationship logb x = log x / log b = ln x / ln b

To calculate log3 of 9, press
9 LOG / 3 LOG =
or
9 LN / 3 LN =

Calculate it as log(9)/log(3) or ln(9)/ln(3). For example, LOG 9 ) / LOG 3 ) = or LN 9 ) / LN 3 ) =

There is no common logarithm function on this calculator. However, you can calculate it easily enough using the natural logarithm function (ln). The log of x is equal to ln(x) / ln(10). In words, calculate the log of a number by calculating its ln then dividing by ln of ten.

log3(u^2/v)
You can move the top as an exponent because of the rules of logs. Then subtracting two same base logs can be combined because another rule. If they are subtracting you divide them and if they adding you multiply them.

The 39g uses its own format for notes. If you want to create notes on your computer, you need to use the Aplet Development Kit, available at http://www.hpcalc.org/details.php?id=5217

Hello,
If you want to do correct mathematics you should strive to use the right words to express the concepts, and the right symbols too. While the logarithm function has an inverse function, it is never called an inverse log and it is never represented as log^-1. (I know you are going to protest and claim that the inverse of a sine function is represented on calculators by sin^-1. This a manufacturer shortcut, and we have no power to change that.) HP uses ASIN, ACOS, ATAN. These are still manufacturer shortcuts but they induce fewer errors.
Anyway, the logarithm functions do have inverse functions.

1. Natural loogarithm (ln)

The inverse of the natural log is the exponential.
ln(e^(x))=e^(ln(x)) =x

2. Common logarithm (logarithm in base 10)
The common logarithm has an inverse function, often called the antilogarithm or antilog.

There is an equivalence.
y=log(x) <--> x=10^(y)

From what I undesrtand of your exemple, you are looking for the antilog of the number -0.4/10 (or -0.04.)

-0.04= log(x), what is x?
You use the equivalence above to look for x as follows.
x=10^(-0.04) =0.9120108394.
Use the change sign (-) not the regular MINUS sign.

Take the log of the last result (still stored in Ans memory) and you get the original number.


Hope it helps.

Hello,
Enter the (positive) number , press [Left Shift: blue][LOG] to calculate log in base 10
12 [Left Shift][LOG] gives 1.079181246.
In general Functions in blue are accessed with left shift. functions in Yellow/Orange are accessed with RIGHT SHIFT.
As to the manual, there is not any around in the Web,except the Spanish version at hp Spain. This is one instance where it pays to speak in (foreign) tongues.
If you want the link, post to this thread and I will be happy to supply it.

Hope it gets you back in gear.

Press SHIFT [ATAN] whatever ENTER

ATAN stands for arctangent (inverse tangent, tan^(-1)) and is the shifted function of the tangent key.