Please don't ask the same question twice in different forums. I answered this over in the other forum.
I calculated 0.2 = e^(-x(ln2/700)) to find x.
But, I could not use a calculator also did not have any approximation for the value of ln.
So, I got x = 700(ln5 / ln2).
But the wolfram says the answer is x = 700((ln5+ 2i pi n) / ln2).
Can I ask where 2i pi n came from?
So, my answer which is just 700(ln5 / ln2) is wrong?
Thanks a lot.