A choir is performing in front of an audience. A microphone is placed in front of the choir to capture sound. Which polar equation represents the microphone the choir is using?

A microphone intended to capture the choir in front while reducing sound from behind has a cardioid polar pattern. The equation r = 4 + 4cos(θ) is a cardioid: it reaches its maximum at θ = 0 and falls to zero at θ = π, so it is strongest in one direction and rejects sound from the opposite direction. Therefore, the correct choice is D, r = 4 + 4cos(θ).

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