Three common-mode emitters 1, 2, 3 are located along a straight line (figure). The distance between emitters 1 and 2 is equal to l/2, and between emitters 2 and 3 - one and a half times greater. The amplitudes of emitters 1 and 2 are the same. What should be the amplitude of emitter 3 so that minima of zero intensity exist in the radiation pattern of the system? Find directions to these minima.

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