d Calculate[r(t) dt d and[ri(t) r(t)] first by differentiating dt the product directly and then by applying the formulas d dt r(t)] ri(t) r(t)] and dr dr [ri(t) r(t)] = r(t) + r(t) and dt dt d dt . [ri(t) x r(t)] = r(t) x + x r(t). dr dr dt dt r(t) = 5ti + 2tj + 7tk,__r(t) = tk 4