A(squared)+B(squared)=C(squared)
This would be A because $100 is the initial amount, and you are adding the amount that arises after (d) days. Since you are adding, it will be the sum. B says product, so you can rule it out. D says difference, so you can rule that out as well. C would be adding the days, not the amount earned each day.
4.8541019662497 + 1.8541019662497 = -3
<span>-4.8541019662497 x 1.8541019662497 = -9</span>
The slope of the tangent line to 
at 
is given by the derivative of at that point:
Factorize the numerator:
We have 
approaching -1; in particular, this means 
, so that
Then
and the tangent line's equation is
