You toss a pebble into a pool of water and watch the circular ripples radiate outward. you find that the function r(t)=12.5 describes the radius of the first circle r in inches after t seconds. the function a (r)=πr^2 describes the area a of the circle. find a (r(t)) when t=2. then interpret your answer. find the area of the circle after 4 s.