if e repersents the something of logarithms then
I memorised e to 16 digits:2.718281828459045...
so that number^2-x^2=0.23
number squred=aprox 7.38906
7.38906-x^2=0.23
subtract 7.38906 forom both sides
-x^2=-7.15906
multiply negative
x^2=7.15906
squre root
2.67564=x