How do I type "log base 3"

There are a couple of different ways

say I want to type in log base 3 of 7

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I could type log37 the highlight the 3, click on [Format] which gives a drop down menu, the click subscript, then click to the end and keep going.

This is the result      log₃7

 

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or I could open the [LaTex Formula] box and type in log_37     Then click  [ok]

This is the result     $$log_37$$

 

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or I could open the [Math Formula] box and type in log(7,3)     Then click  [ok]

This is the result     $${{log}}_{{\mathtt{3}}}{\left({\mathtt{7}}\right)}$$

 

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I use LaTex mostly because it is very versatile, you can use it for just about everything.  But the other two methods are more basic and easy to use.