At time t1 = 2.00 s, the acceleration of a particle in counterclockwise circular motion is (1.00 m/s2) i + (6.00 m/s2) j. It moves at constant speed. At time t2 = 4.00 s (3/4 of a revolution later), its acceleration is (6.00 m/s2) i + (-1.00 m/s2) j. What is the radius of the path taken by the particle?