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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).