? QUESTION The number of bacteria in a culture decreases according to a continuous exponential decay model. The initial population in a study is 400 bacteria, and there are 140 bacteria left after 6 minutes. (a) Let \( t \) be the time (in minutes) since the beginning of the study, and let \( y \) be the number of bacteria at time \( t \). Write a formula relating \( y \) to \( t \). Use exact expressions to fill in the missing parts of the formula. Do not use approximations. \( y=\square \)

Write the complex number in trigonometric form \( r(\cos \theta+i \sin \theta) \), with \( \theta \) in the interval \( \left[0^{\circ}, 360^{\circ}\right) \). \[ -3 \sqrt{3}+3 i \] \( -3 \sqrt{3}+3 i=\square\left(\cos \square^{\circ}+i \sin \square^{\circ}\right) \) (Type the value for \( r \) as an exact answer, using radicals as needed. Type the value for \( \theta \) as an intege as needed.)

Find the following product, and write the product in rectangular form, using exact values. \( \left[8\left(\cos 90^{\circ}+i \sin 90^{\circ}\right)\right]\left[3\left(\cos 30^{\circ}+i \sin 30^{\circ}\right)\right] \) \( \left[8\left(\cos 90^{\circ}+i \sin 90^{\circ}\right)\right]\left[3\left(\cos 30^{\circ}+i \sin 30^{\circ}\right)\right]=\square \) \( ( \) Type your answer in the form \( \mathrm{a}+\mathrm{bi} \).

Find the standard form of the equation of the hyperbola satisfying the given conditions. Foci at \( (-7,0) \) and \( (7,0) \); vertices at \( (3,0) \) and \( (-3,0) \)

Find the standard form of the equation of the hyperbola satisfying the given conditions. Foci at \( (0,-8) \) and \( (0,8) \); vertices at \( (0,3) \) and \( (0,-3) \)

Suppose the half-life of a drug in the bloodstream is 9 hours. To the nearest milligram, how much of the drug is left in the bloodstream 20 hours after a 260 milligram dose? 56 milligrams 32 milligrams 190 milligrams 117 milligrams