I know it reflects off the side because this would give a smaller angle to the horizontal (which is what the question is asking me to optimize for). I am unsure about how I would find an angle, and where the light would reflect off of if it was not at half the height.
Homework Statement
At the aquarium where you work, a fish has gone missing in a 10.5m -deep, 9.45m -diameter cylindrical tank. You shine a flashlight in from the top edge of the tank, hoping to see if the missing fish is on the bottom. What’s the smallest angle your flashlight beam can make...