Bit of a maths problem, find r given that:
100 = 8e^(-r) + 8e^(-2r) + 108e^(-3r)
A full worked solution would be apprieciated, thanks.
Let x = e-r, then the equation can be written as:
8x + 8x2 + 108x3 - 100 = 0
This factors as 4(27x - 25)(x2 + x + 1) = 0
The only real root is x = 25/27
so e-r = 25/27 or r = ln(27/25) or r ≈ 0.077
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Thanks for that, never even occured to me to try it that way, too busy trying to take logs.
