Explain in detail how /2 is the minimum angle, and with what method is this found. Why is this method used?

Part I: Complete the following steps:

A lifeguard is at point A of a circular pool with diameter 40 m. He must reach someone who is drowning on the exact opposite side of the pool, at position C. The lifeguard swims with a speed v = 3 m/s from point A to point B, and then runs around the pool from point B to point C at speed w = 9 m/s.

1. Find a function that measures the total amount of time it takes to reach the drowning person as a function of the swim angle, expressed in radians.
2. Find at what angle , in radians, the lifeguard should swim to reach the drowning person in the least amount of time.