4. The concentration of testosterone (in \( ng / dL \) ) in an adult male's blood follows a sinusoidal function with \( 535 ng / dL \) being the maximum concentration and \( 465 ng / dL \) being the minimum. The time it takes to go from maximum to minimum is \( 3 \) hours. Assume there is a maximum at \( t = 0 \) .
i) Determine the equation that models it using \( \cos ( t ) \) .
ii) Graph the concentration of testosterone versus time. Make sure you label your graphs correctly for full marks.