Question 81524
The logarithm, base 2, of 1/16.

In other words:  What exponent of 2 is 1/16?

Finding a logarithm is basically the opposite of finding a power.

In other words:  Solve this equation for {{{y}}} : {{{2^y = 1/16}}}

Here are some examples of exponents of 2:

{{{2^5 = 32}}}
{{{2^4 = 16}}}
{{{2^3 = 8}}}
{{{2^2 = 4}}}
{{{2^1 = 2}}}
{{{2^0 = 1}}}
{{{2^-1 = 1/2}}}
{{{2^-2 = 1/4}}}
{{{2^-3 = 1/8}}}
{{{2^-4 = 1/16}}}
That last one is the one you want ...

The answer is: {{{log_2 (1/16) = -4}}}