Write the Word or Phrase That Best Completes Each Statement $$d = 25 \cos \left( \frac { 3 \pi } { 4 } t \right)$$

Essay

Write the word or phrase that best completes each statement or answers the question.
-A boy is flying a model airplane while standing on a straight line. The plane, at the end of a twenty-five foot wire, flies in circles around the boy. The directed distance of the plane from the straight line is found to be
$$d = 25 \cos \left( \frac { 3 \pi } { 4 } t \right)$$ where d is measured in feet and t is the time in seconds. If d > 0, the plane is in front of the boy; if d < 0, the plane is
behind him.
What is the amplitude? What is the period?
Graph d over two periods beginning at t = 0.