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1.8.8 Integration by substitution (A-level only)

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Question 47

The rate of power consumption, P(t)P(t)P(t) in kilowatts, of an industrial cooling system is modeled by the function

P(t)=18t+45e2t+5 P(t) = \sqrt{18t+45} e^{\sqrt{2t+5}} P(t)=18t+45​e2t+5​

where t≥0t \ge 0t≥0 is the time in hours since the start of the shift.

a.

By using the substitution u=2t+5u = \sqrt{2t+5}u=2t+5​, show that the total energy consumed in the interval 2≤t≤102 \le t \le 102≤t≤10, given by ∫210P(t) dt\int_{2}^{10} P(t) \, dt∫210​P(t)dt, can be expressed in the form

∫abku2eu du \int_{a}^{b} k u^2 e^u \, du ∫ab​ku2eudu

where aaa, bbb and kkk are integers to be found.

[5]
b.

Hence find, by algebraic integration, the exact value of the total energy consumed between t=2t = 2t=2 and t=10t = 10t=10, giving your answer in the form pe5+qe3p e^5 + q e^3pe5+qe3 where ppp and qqq are integers.

[5]

1.8.8 Integration by substitution (A-level only) Questions

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