The completed construction of a regular hexagon is shown below. Explain why ACF is a 30º-60º-90º triangle.

To solve the problem we must know about Thales' theorem and a regular hexagon.
As we know according to the Thales' theorem which states that if A, B, and C are distinct points on a circle where the line BC is a diameter, the angle BAC is a right angle.
ΔACF is a 30º-60º-90º triangle.
The line FC is the diameter of the circle and hypotenuse as well, so ∠FAC = 90.
For a regular hexagon, each of its angles measures 120°. So, in the figure, ∠EFA = 120°, but also at the same time line FC is bisecting the ∠EFA which means ∠CFA will be equal to 60° in ΔFAC.
Further, the sum of all the angles of a triangle is always 180°.
Hence, ΔACF is a 30º-60º-90º triangle.
Learn more about Thales' theorem:
https://brainly.com/question/14417137