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3.6.2 Differentiation (A-level only)

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Question 7

The concentration of a specific catalyst in a bioreactor, C C\,C mg/L, is monitored over a 12-hour production cycle. The concentration at time t t\,t hours, for 0≤t≤120 \le t \le 120≤t≤12, is modeled by the function:

C=t20(24+10t−t2)+5 C = \frac{\sqrt{t}}{20}(24 + 10t - t^2) + 5 C=20t​​(24+10t−t2)+5

Given that C C\,C has a stationary value at t=αt = \alphat=α:

a.

Use calculus to show that α \alpha\,α satisfies the equation

5α2−30α−24=0 5\alpha^2 - 30\alpha - 24 = 0 5α2−30α−24=0
[4]
b.

Hence find the value of α\alphaα, giving your answer to 3 decimal places.

[2]
c.

Use further calculus to prove that C C\,C is a maximum at this value of α\alphaα.

[3]

3.6.2 Differentiation (A-level only) Questions

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