(Solved): Please explain clearly with every steps' formuls. Problem 4.2: The reluctanc ...

Please explain clearly with every steps' formuls.

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Problem 4.2: The reluctance of a two-pole reluctance motor varies with displacement angle $$?$$ according to the following expression: $$\mathcal{R}(?)=5000?1500\cos 2?{\mathrm{H}}^{?1}$$ If the number of turns in the coil is $$N=1,000$$, instantaneous coil current is $$i=10\mathrm{A}$$, and the displacement angle $$?$$ is $$15^{?}$$, how much is the instantaneous torque developed by the motor?