how can you simplify this??

log10(10^.5)

log10 as in log base 10

By definition:

Log_10[10^(x)] = x

ok, but it is 10 to the 1/2 power, not x
how would you simplify it then?

That's then the special case of x = 1/2:

If for all x:

Log_10[10^x] = x,

then for x = 1/2 this implies:

Log_10[10^(1/2)] = 1/2