What is the minimum of the sinusoidal function?

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Step-by-step explanation:

The amplitude of a sinusoidal function is one-half of the positive difference between the maximum and minimum values of a function. It is simply the vertical distance from the x-axis (or midline) to the highest (or lowest) point on the curve.

cross multiplying, we get :

⇒ (3) × (5) = (9) × (x)

⇒ 15 = 9x