page 07 MARKS 12. A curve, for which 3 8 3 dy x dx  , passes through the point (−1, 3). Express y in terms of x. 13. A patient is given a dose of medicine. The concentration of the medicine in the patient’s blood is modelled by 0.0053 11 t t C e  where: • t is the time, in minutes, since the dose of medicine was given • Ct is the concentration of the medicine, in mg/l, at time t. (a) Calculate the concentration of the medicine 30 minutes after the dose was given. The dose of medicine becomes ineffective when its concentration falls to 0.66 mg/l. (b) Calculate the time taken for this dose of the medicine to become ineffective. [Turn over 4 1 3