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There are two more laws of logarithms which we need to be able to use.

There is the addition law:

loga(x)+loga(y)=loga(xy)

and the subtraction law

loga(x)loga(y)=loga(xy)

It is important to note that we can't directly use these laws if the functions have a coefficient in front. For example,

2log(5)3log(3)

needs to first be changed, using the power law, into

log(52)log(33)

Now we can use the subtraction law:

log(2527)

Let's see some more examples!


  1. Assuming x>0, simplify

    2log4(x)3log4(x)
  2. Express

    logu(uvw3)

    in terms of logv(u) and logv(w).