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Question 70

The surface area SSS (measured in cm2\text{cm}^2cm2) of a particular fungus culture is observed over time ttt (measured in hours). The growth of the culture is modeled by the differential equation

dSdt=8tS1/2e2t,S≥0,t≥0 \frac{\text{d}S}{\text{d}t} = \frac{8t S^{1/2}}{\text{e}^{2t}}, \quad S \ge 0, \quad t \ge 0 dtdS​=e2t8tS1/2​,S≥0,t≥0
a.

Given that the initial surface area of the fungus is 9 cm2 at t=0t = 0t=0, solve this differential equation to find S1/2S^{1/2}S1/2 in terms of ttt, giving your answer in the form S1/2=g(t)S^{1/2} = g(t)S1/2=g(t).

[6]
b.

Hence find the equation of the horizontal asymptote to the curve with equation S1/2=g(t)S^{1/2} = g(t)S1/2=g(t).

[2]

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