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1 Unit 1: Pure Mathematics A

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Question 365

The torque τ \tau\,τ in a precision galvanometer is given by the interaction of two magnetic fields. For the system to be in equilibrium at an angle α\alphaα, the following condition must be met:

5cos⁡α+3=4sin⁡αtan⁡α 5\cos \alpha + 3 = 4\sin \alpha \tan \alpha 5cosα+3=4sinαtanα
a.

Show that this condition can be rewritten as the quadratic equation

9cos⁡2α+3cos⁡α−4=0 9\cos^2 \alpha + 3\cos \alpha - 4 = 0 9cos2α+3cosα−4=0
[3]
b.

A specific test run observes the system over the time interval 0≤t<π0 \le t < \pi0≤t<π, where the angle is driven such that α=2t\alpha = 2tα=2t. Determine the times t t\,t at which 5cos⁡(2t)+3=4sin⁡(2t)tan⁡(2t)5\cos(2t) + 3 = 4\sin(2t) \tan(2t)5cos(2t)+3=4sin(2t)tan(2t), giving your answers to 2 decimal places.

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1 Unit 1: Pure Mathematics A Questions

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