1. What is the range of frequencies a human ear can hear?

Humans can detect sounds in a frequency range from about 20 Hz to 20 kHz.

(Human infants can actually hear frequencies slightly higher than 20 kHz, but lose some high-frequency sensitivity as they mature; the upper limit in average adults is often closer to 15–17 kHz.)

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step-by-step explanation:

sine over hypotenuse

cosine   equals adjacent

tangent over hypotenuse