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Differentiation

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Question 434

The intensity, III, of a specialized acoustic wave at a distance rrr from the source is modeled by the equation:

I=rsin⁡(2r),r>0,I>0 I = r^{\sin(2r)}, \quad r > 0, \quad I > 0 I=rsin(2r),r>0,I>0
a.

By first taking natural logarithms, find an expression for dIdr\frac{dI}{dr}drdI​ in terms of III and rrr.

[5]
b.

Hence show that at any stationary point of the intensity, the distance rrr must satisfy the equation:

tan⁡(2r)+2rln⁡r=0 \tan(2r) + 2r \ln r = 0 tan(2r)+2rlnr=0
[3]
Markscheme

Differentiation Questions

  1. A Level
  2. /Maths
  3. /Differentiation

717 exam-style questions on Edexcel A Level Maths Differentiation, covering 9.1 Differentiating sin x and cos x, 9.2 Differentiating exponentials and logarithms, 9.3 The Chain Rule, 9.4 The Product Rule, 9.5 The Quotient Rule, 9.6 Differentiating Trigonometric Functions, 9.7 Parametric Differentiation, 9.8 Implicit Differentiation, 9.9 Using Second Derivatives, and 9.10 Rates of Change. Each one has a worked solution and a mark scheme showing where the marks go.

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