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Trigonometry and Modelling

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Question 46

An optical sensor measures the angular deflection ϕ \phi\,ϕ of a light beam. During a calibration test, the system reaches equilibrium when the following relationship is satisfied:

7tan⁡ϕ=4cos⁡ϕ 7 \tan \phi = 4 \cos \phi 7tanϕ=4cosϕ
a.

Show that this equilibrium condition can be expressed as the quadratic equation

4sin⁡2ϕ+7sin⁡ϕ−4=0 4 \sin^2 \phi + 7 \sin \phi - 4 = 0 4sin2ϕ+7sinϕ−4=0
[3]
b.

A specific configuration of the sensor requires that the deflection varies such that ϕ=3ψ\phi = 3\psiϕ=3ψ. Determine all possible values of ψ \psi\,ψ in the range 0∘≤ψ≤60∘ 0^\circ \le \psi \le 60^\circ\,0∘≤ψ≤60∘ that satisfy the equilibrium condition:

7tan⁡(3ψ)=4cos⁡(3ψ) 7 \tan(3\psi) = 4 \cos(3\psi) 7tan(3ψ)=4cos(3ψ)

Give your answers to 2 decimal places.

[4]

Trigonometry and Modelling Questions

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