1. The problem statement, all variables and given/known data Let v1 be the velocity of light in air and v2 the velocity of light in water. According to Fermat's principle, a ray of light will travel from a point A in the air to a point B in the water by a path ACB that minimizes the time taken. 2. Relevant equations @=angle sin(@1)/sin(@2)=v1/v2 @1= the angle of incidence @2= the angle of refraction 3. The attempt at a solution What is known: 1.) v1 and v2 are constants 2.) horizontal distance from A to B are constants 3.) t=d/v v=dt derivative of velocity= (AC)t if the distance from the water to A is x and the distance from the water to B is y and x and y are constants then t=csc@1x/v1 +csc@2y/v2 using this equation and the known variables i am not sure where to go from here.