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jstavitsky1-Visitor
1-Visitor
Aug 12, 2014 1:08 PM UTC
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Input logarithms with a fractional base

Probably newbie question

Is it possible to input logarithms with a fractional base? When I try it creates a rational expression. Parentheses don't work either. Or, must I change the base?

Thanks

Joe

Werner_E
Werner_EAnswer
25-Diamond I
Aug 12, 2014 1:25 PM UTC

Joseph Stavitsky wrote:

Probably newbie question

Is it possible to input logarithms with a fractional base?

Yes, as long as the base is positive and does not not equal one.

When I try it creates a rational expression.

What do you mean by that and why do you think thats not as it should be?

Parentheses don't work either. Or, must I change the base?

You don't show what you do and don't say what you expect, so we can't tell. Obviously when you want the logarithm of a base unequal to 10 you have to state that.

You know that in Mathcad log(a) means the logarithm of a to base 10, while log(a,b) ist the logarithm to base b of a.

If you want to take the logarithm of base 2/3 from an argument like 27/8 (which is obviously -3), you would type log(27/8, 2/3)=

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4 replies

LucMeekes23-Emerald V
23-Emerald V
Aug 12, 2014 1:22 PM UTC

Hi Joseph,

One example of a logarithm with a fractional base is the natural logarithm ln(x), with base 2.71828182845....

A logarithm of a value x (> 0) to any base b (> 0) can be computed as ln(x)/ln(b).

Or do you mean something else...?

Luc

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Werner_E
Werner_E25-Diamond I
25-Diamond I
Aug 12, 2014 1:42 PM UTC

LucMeekes wrote:

Hi Joseph,

One example of a logarithm with a fractional base is the natural logarithm ln(x), with base 2.71828182845....

A logarithm of a value x (> 0) to any base b (> 0) can be computed as ln(x)/ln(b).

Any base but b=1!

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Werner_E
Werner_E25-Diamond IAnswer
25-Diamond I
Aug 12, 2014 1:25 PM UTC

Joseph Stavitsky wrote:

Probably newbie question

Is it possible to input logarithms with a fractional base?

Yes, as long as the base is positive and does not not equal one.

When I try it creates a rational expression.

What do you mean by that and why do you think thats not as it should be?

Parentheses don't work either. Or, must I change the base?

You don't show what you do and don't say what you expect, so we can't tell. Obviously when you want the logarithm of a base unequal to 10 you have to state that.

You know that in Mathcad log(a) means the logarithm of a to base 10, while log(a,b) ist the logarithm to base b of a.

If you want to take the logarithm of base 2/3 from an argument like 27/8 (which is obviously -3), you would type log(27/8, 2/3)=

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jstavitsky1-VisitorAuthor
1-Visitor
Aug 12, 2014 1:39 PM UTC

That last part is what I was missing, thanks. I was trying to input it as it is traditionally typeset.

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