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jstavitsky1-Visitor
1-Visitor
August 12, 2014
Solved

Input logarithms with a fractional base

  • August 12, 2014
  • 4 replies
  • 1751 views

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

Best answer by Werner_E

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)=

4 replies

L
LucMeekes23-Emerald IV
23-Emerald IV
August 12, 2014

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

Werner_E
Werner_E25-Diamond I
25-Diamond I
August 12, 2014

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!

Werner_E
Werner_E25-Diamond IAnswer
25-Diamond I
August 12, 2014

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)=

J
jstavitsky1-VisitorAuthor
1-Visitor
August 12, 2014

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

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