Question about Texas Instruments TI-84 Plus Calculator

# How do I key in log and inverse log at the same time?

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There are very few instances where you have two press two keys AT THE SAME TIME, the most notable of them is when you want to force the calculator into the BOOT SCREEN. Most key combinations are key sequences, meaning you press a key and THEN press another.

This said, let us get back to your question.

When you apply a function on an expression, then apply the inverse of the function on the result you get the original expression back.
If f is a function and f^-1 its inverse, by definition f^-1[f(x)]=f[f^-1(x)] =x
As you can see you do not need a calculator to find the result.

Concerning the logarithmic functions

For the natural logarithms (logarithms in base e) labeled [ln], the inverse of the logarithm is the exponential function e^
ln[e^(x)] =e^[ln(x)] =x

For the common logarithms (logarithms in base 10), labeled [log], the inverse function of the log is the raising 10 to the power of. It is usually called the antilogarithm or antilog.

y= log(x) is equivalent to x=10^(y)

Try the following exemple

log(14) = 1.146128036
10^(1.146128036) =14

To access the 10^x function you press [2nd][LOG]
To access the exponential function you press [2nd][LN]

Posted on Jan 20, 2010

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Posted on Jan 02, 2017

If I understand you correctly, the inverse of the log operation is exponentiation. So if your log = x, the inverse is 10 raised to the x power. On most TI calculators this is on the same key as the log function.

michael

Posted on Jun 13, 2008

Press "2nd LN" which gives you the exponential (inverse natural log) of 7.41 = 1652.426....

Pressing LN will give you back 7.41

Same procedure to use logs to base 10, use LOG and 2nd LOG

Posted on Dec 31, 2008

Hi,
Sorry to contradict you but there are many types of logarithms, the most important ones are

2. the natural logarithms (logarithms in base e)
3. the binary logarithms (logarithms in base 2)
On calculators, the common logarithms are labeled [LOG], and the natural logarithms are labeled [LN].

The inverse function of the natural log function is the exponential (e^(x)), and the inverse of the log in base ten function is the function ten to the power of. It is called (sometimes) the antilog

Ex:
Question What is the antilog of 3.5678?
Answer The antilog of 3.5678 is 10^(3.5678) = 3696.579068
Verification: log(3696.57908) =3.5678

Hope it helps.

Posted on Nov 29, 2009

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## Related Questions:

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The inverse of log functions are power functions.
Inv of ln is exponential (e^x)
A function and its inverse usually share the same physical key. One function is accessed directly, the other by using the SHIFT or 2ndF key.

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The inverse of the log function is the function 10^
y=log(x) has the function x=10^y as inverse.
y=ln(x) has the function x=e^y
log and 10^ have the same key.
ln and e^ have the same key.

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The inverse common log is the shifted function of the "log" key. The inverse natural log is the shifted function of the "ln" key.

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The inverse common logarithm is the shifted function of the "log" key, the inverse natural logarithm is the shifted function of the "ln" key.

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### Where is the antilog

The antilog ( Oh I hate this word) is the inverse function of the log. If you are talking about base 10 log (common logarithms) the antilog is the power of 10 function.( 10^x) If you are talking about the natural log (ln) the antilog is the exponential function e^x.
On most calculators, a mathematical function and its inverse share the same physical key. One function is marked on the key and the inverse on the faceplate. One is accessed directly by pressing the marked key, and its inverse is accessed by pressing 2ndF, 2nd of SHIFT followed by the key.
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### Hi, how do i calculate log^-1(-2) on my ti-30xa? thank u.

The inverse of the log function is the power function.
For log in base 10 that inverse is 10 to a power of
More generally, let b be the base of the logarithm. If y=log_b (x) then x=b^y
For your case log=log_10, to calculate the inverse you perform 10^(-2)=0.01=1/100
On calculators the log in base 10 and its inverse share the same physical key. One is accessed directly, the other is the shifted key function.

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Depending on the actual log function you are talking about, the inverse function (what you call the anti log) can be one of several things.
The inverse of the natural log (LN) is the exponential function e^x.
If y= ln(x) then x=e^y
On a calculator functions that are inverse of one another share the same physical key. If one function is marked on a key, the inverse function is usually the SHIFTED (or 2nd) key
The inverse of the common (decimal logarithm) is the power function with 10 as base.
Example: if y= log(x) then x=10^y
For an arbitrary base (must be positive) if y= log_b(x) then x=b^y.
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Press the log key, enter a poistive number and press the = key.
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The log base 10 function has an inverse: It is the 10 ^x function. It shares the same physical key with the decimal log. Use [SHIFT][LOG].
The natural log (LN) has an inverse alos and that it the exponentila function e^x. It shares the same physical key with it.

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