SCalc92.5.079.A Cepheid variable star is a star whose brightness alternately increases and decreases. For a certain star, the interval between times of maximum brightness is 3.9 days. The average brightness of this star is 3.0 and its brightness changes by 0.25. Using this information, the brightness of the star at time t, where t is measured in days, has been modeled by the functionB(t)=3.0+0.25 sin2t3.9.(a)Find the rate of change of the brightness at time t days.