How do I find the number whose common logarithm is 2.6025?

1 Answer
Jul 14, 2015

Can use log_10(2) ~= 0.30103log10(2)0.30103 to find approximate value 400400 then multiply by an approximation for 10^0.00044 ~= 1.001100.000441.001 to get 400.4400.4.

If you have a calculator then just 10^(2.6025) ~= 400.4055102.6025400.4055

Explanation:

10^(2.6025) = 10^2*10^0.60206*10^0.00044102.6025=102100.60206100.00044

~=100*10^(2log_10(2))*10^0.00044100102log10(2)100.00044

=100*2^2*10^0.00044=10022100.00044

=400*10^0.00044=400100.00044

Now

1.001^1000 = (1+0.001)^10001.0011000=(1+0.001)1000

=1+((1000),(1))0.001+((1000),(2))0.001^2+...

=1+1+0.4995+0.166167+0.04141712475+...

somewhere between 2.7 and 3

log_10(3) ~= 0.4771 (one of those useful numbers to memorise)

log_10(2.7) = log_10(27/10) = log_10(3^3/10) = 3log_10(3)-1

~= 0.4313

So 0.4313 < 1000 log_10(1.001) < 0.4771

0.0004313 < log_10(1.001) < 0.0004771

So 1.001 is a fairly good approximation for 10^0.00044